What is a bypass and why is it needed: we study the functional features and installation rules. Bypass - what is it and what is it for? Bypass line device

To everyone who has even a little experience with engineering networks, you are probably familiar with the term “bypass”. In simple words, this is a bypass line through which water can flow due to various circumstances. In the article we will consider these circumstances and understand what role the bypass plays in the heating and water supply system. We will also show you how to install it correctly with your own hands if necessary.

Bypass functions in the heating system

Let us clarify that a bypass is a pipeline designed to allow water to flow bypassing a certain section of the main line where some equipment is installed. In heating circuits it can be found in two places:

• in single-pipe systems as a jumper on radiators;
• on distribution manifold water heated floors.

As is known, in single pipe system heating, the heat transfer of the first battery affects the operation of the next one and so on. This applies to both vertical and horizontal layouts. If a bypass is not installed in the heating system, the radiators will be switched on in series. As a result, the first one will select maximum amount heat, the second is all that remains, and the third will receive only the cooled coolant.

To prevent this from happening, the supply and return near each battery are connected by a jumper, whose task is to direct part of the coolant bypassing the radiator. IN in this case The principle of operation of the bypass is to transfer the same part of the heat to near and far heating devices and reduce their dependence on each other. How this is implemented can be seen in the figure:

Important. In the shown vertical system the bypass device is designed so that the diameter of the pipe is smaller than the main line and slightly offset from its axis to the side. The goal is to prevent the coolant from passing in a straight line under the influence of gravity, past the radiator. In a horizontal system, the main pipe itself is a bypass, while it does not shift anywhere and remains the same flow area everywhere.

In a heating system, a bypass is needed to distribute heat evenly across the radiators, as well as to perform their repair or maintenance. If for some reason you need to disconnect and remove heating device, then it is enough to simply turn off the 2 taps installed at the inlet and outlet of the coolant. Then the water will follow a bypass path through the jumper.

But the heating bypass on the water heated floor manifold plays a different role. Here the bypass line is part of a mixing unit with a three-way valve. The task of the unit is to prepare the coolant required temperature for supply to heating circuits of underfloor heating. Indeed, in these circuits the water temperature does not exceed 45 ºС, while in the supply line it can be 80 ºС.

IN normal mode a three-way valve allows hot water from the system to the heated floor in a limited amount. The rest of the coolant passes through this automatic bypass and mixes with cold water from the collector and returns back to the boiler. Since the temperature difference in the main and collector is significant, the bypass line is used constantly. It turns out that without it normal functioning underfloor heating impossible.

Bypass in the boiler room

In boiler piping schemes, a bypass line is also necessary in 2 cases:

• as a bypass for a circulation pump;
• for organizing a small circulation circuit for a solid fuel boiler.

A pump installed on a bypass pipeline is found in heating systems quite often, sometimes even without special need. The fact is that single-pipe or two-pipe system heating system, originally conceived with forced circulation, will never be able to function when the pump is turned off. It does not have large slopes and increased pipe diameters for this. But a bypass for the pump is precisely what is needed so that water can flow in a straight line while the pumping device is not working.

Hence the conclusion: when connecting a system designed for forced circulation to a boiler, there is no need to install the pump on the bypass. Disabling and removing the unit will in any case stop the movement of the coolant, so the pump is installed in a straight line.

Another thing is a system adapted for natural movement water. It often happens that in order to increase efficiency, a pump is not simply built into it, but a bypass system with a check valve is installed in the direct line. This allows, in the event of a power outage, to automatically switch to natural circulation, which is reflected in the diagram:

While the pump is running, it presses the valve with its pressure reverse side and does not allow the flow to flow in a straight line. As soon as you turn off the power or turn off one of the taps, the pressure will disappear and the bypass valve will open a direct path for the coolant, convective movement of water will be restored. You can safely remove the pump or clean the sump; this will not disrupt the operation of the system, it will simply switch to a different mode.

Well, the last place to use the bypass is the small circulation circuit of a solid fuel boiler with a mixing unit. Here, a jumper connected to a three-way valve allows the heat generator to warm up to a temperature of 50 ºC in order to avoid exposure low temperature corrosion on the steel walls of the firebox. In this case, the bypass circuit looks like this:

The principle of operation is simple: the valve does not allow entry into the boiler cold water from the system until the coolant circulating through the bypass line reaches the required temperature. Then the valve opens and lets cold water into the circuit, mixing it with hot water. Then condensation does not form on the walls of the firebox and corrosion does not occur.

Sometimes a bypass is still needed in the water supply system. For example, to remove a heated towel rail in the bathroom for repair, cleaning or replacement. Because it connects to DHW riser, then in an apartment building its dismantling will create a lot of inconvenience. It’s easier to foresee this in advance and install a jumper with a tap when installing the heater.

How to install the bypass correctly

The distribution unit for underfloor heating also includes a bypass line, but this is a topic for another discussion. As for jumpers on a one-pipe system, their installation is very simple and is carried out already during the installation of the system, since without them the latter will not work correctly. It is not much more difficult to install a bypass line with a circulation pump yourself. It is enough to have a regular set of tools and study the diagram:

Advice. In order not to collect all the parts separately, you can buy a ready-made assembly, shown in the figure below:

Installing a bypass for a heated towel rail is also not difficult. For connections you can take metal-plastic pipes, and also purchase taps, tees and bends. Perform assembly in accordance with the diagram:

Conclusion

It turns out that a simple piece of pipe, which is a bypass line, can play an important role in many cases. Here it ensures the operation of the system, there it helps distribute heat, and sometimes protects the equipment. In all of the above cases, you cannot do without a bypass.

It was an unpleasant surprise for the Pushchino residents new stage works of Teplovodokanal. An obstacle to passage has appeared on another part of the Arbat - an external bypass line is being created. The director of Teplovodokanal, Albert Ryabov, spoke about the reasons, plans and timing.

For many Pushchino residents, life was divided into “before” and “after”, or rather, their path was divided into “before” and “later”. The main street of the city is blocked by a temporary line. The reason for this is the replacement of the main hot water supply line, the pipes in which have long since expired.
Albert Ryabov, director of the municipal unitary enterprise "Teplovodokanal": "The government of the Moscow region has allocated money to replace these pipes. Competitive procedures are now underway to replace this route. In order not to disconnect residents from hot water supply and, accordingly, heating, external network a bypass to which all neighborhoods and all houses will be connected. After this there will be an opening of the Arbat and replacement underground heating main. By the spring of the pipe external gasket will be removed completely. And the coverage on Arbat has been restored."
Among the questions posed by Pushchino residents, the leading one is: “Why is work carried out before winter?”
Albert Ryabov, director of the Teplovodokanal municipal unitary enterprise: “Actually, it doesn’t matter when such work is carried out. Whether in winter or summer, we still need to build a bypass line.”
The answer to one of the age-old questions “What to do?” everyone searches for themselves. There were those who, at the risk of injury, made their way under or, worse, over pipes installed on the slabs. Recently, a crossing was installed in front of the store. But soon the townspeople will have only one way - to bypass the obstacle. Most likely, the structure will have to be removed due to the foundation pit. But, as Albert Ryabov explains, everything will depend on the production of work.
Albert Ryabov, director of the municipal unitary enterprise "Teplovodokanal": "Unfortunately, when working to replace this network, it will be impossible to cross this network. Since, firstly, the bypass line is quite high from the ground - about 10 meters from the ground, but a wide part will still be opened Arbat, the wide part of the path. There will be a very large pit the entire length of the Arbat, and it is impossible to cross the pit and, accordingly, the pipes. At the same time, you must understand that it is still necessary to ensure the passage of equipment. bridge, it must be higher than passing equipment, that is, about 4 meters high.”
The cost of one such crossing, which then cannot be used anywhere else, is estimated at 500-700 thousand rubles; this, according to the director, is not adequate for the inconvenience. The construction of a U-shaped arch costs about 300 thousand rubles, and the problem of overcoming the pit will still remain. Therefore, according to Albert Ryabov, there is only one conclusion - the obstacle must be circumvented.
Albert Ryabov, director of the Teplovodokanal municipal unitary enterprise: “Yes, this will cause a large number of"There are no complaints, but the city is small and the neighborhood is not large, and a detour of 300-400 meters should not cause any particular complaints."
The first bypass option is near the former Steklyashka store. The line will end near Kuznetsov Square.
Albert Ryabov, director of the Teplovodokanal municipal unitary enterprise: “Just opposite the field near the hotel, it will dive underground, meaning it will have to go around to this field.”
The director of Teplovodokanal believes that the situation with the bypass line will last about three months. The deadline “by spring” applies to the entire complex of works; the bypass line will be removed earlier, as soon as the replaced heating network is launched.
Albert Ryabov, director of the Teplovodokanal municipal unitary enterprise: “This spring it will be cleaned only because restoration work covering the Arbat cannot be done in winter, it cannot be done in frosty weather. Frosts and winter will not prevent you from filling the pit back and, accordingly, filling it with crushed stone. That is, in fact, most likely, in winter there will already be a covering in the form of crushed stone on the Arbat, that is, it will be possible to walk.”
Treat the workaround as an outrageous problem or as a additional opportunity walk around the city? Everyone will choose the answer to this question themselves. Albert Ryabov appealed to the Pushchino residents with a request to be tolerant of the situation.
Albert Ryabov, director of the municipal unitary enterprise “Teplovodokanal”: “Not all cities and not always are allocated such large funds for such large replacements, and I believe that you can endure the inconvenience of replacing this network. I can tell everyone that I also have a child studying in gymnasium, and we walk along this Arbat every day."
“Teplovodokanal”, which has now become for Pushchino residents both a symbol of discontent and hope for warmth, calls for an understanding attitude towards the current situation. And Voltaire also said that there are no great things without great difficulties.

Diana Larionova, Andrey Mikhailin, TVS Pushchino

A bypass is a bypass line through which water can flow. In our article we will look at what the bypass is used for, as well as the functions and rules for installing the device.

Bypass functions in a heating system

A bypass is a pipeline that is used to flow water bypassing any section of the main line.

In the heating system it is installed in the following places:

1. In the water warm floors it is installed on the distribution manifold.
2. In a single-pipe heating system, a bypass is installed on the radiator as a jumper.

Regardless of whether your heating scheme is horizontal or vertical, the heat transfer from one battery affects the next, etc. If there is no bypass in the system, then the maximum amount of heat will be in the first radiator, and an ever smaller amount will be supplied to the subsequent ones. In order to avoid this situation, it is necessary to connect the supply and return pipes with a jumper near each battery. And it, in turn, directs a certain amount of coolant bypassing the battery.

Using a bypass, the same amount of heat will be distributed to all heating radiators.

A bypass is also necessary for maintenance and repair of the system. If it is necessary to disconnect and remove the heating device, you can turn off the two taps that are installed at the inlet and outlet of the coolant. In this case, the water will bypass through the jumper.

In a water heated floor system, the bypass functions are different. The bypass line is part of the node three way valve. The function of the unit is to heat the coolant to the required temperature. And it gets into the heating circuits of the heated floor.

The temperature in the circuits cannot be more than 45°. And in the supply line it can reach 80°.

At regular work hot water from the system reaches the floor in small quantities. And the rest of the coolant passes through the bypass and mixes with cold water from the collector. And then returns to the boiler. Since there is a large temperature difference between the collector and the main, the bypass line operates constantly. Therefore, without a bypass, normal operation of a water heated floor system is impossible.

Pump types and bypasses

When installing this device, you need to pay attention to the type of pump that is used in the heating system. The unit is installed on the main highway.

There are two types of pumps:

1. "Wet". In this type, the rotor impeller is arranged in water. The wet type pump can be installed on the return and supply pipes.
2. "Dry". The rotor in such a pump does not come into contact with the coolant. The disadvantage of a dry type pump is noise during operation. Therefore, it is advisable to use it in a boiler room with good sound insulation. The unit can be installed on the return pipeline.

Bypass installation

You can install a jumper in a single-pipe system during the installation of a heating system for its quality work. Bypass device simple process. You can install a bypass line with a circulation pump yourself after studying the diagram, and you also need to purchase the simplest set of tools. And also for ease of installation, it is recommended to purchase a ready-made assembly. Then you won't have to assemble each part separately.

Bypasses are also installed on heated towel rails. The installation process is not difficult. For installation, you will need to buy bends, taps, tees, and you can also use metal-plastic pipes for connections.

Bypass in the boiler room

A bypass line is sometimes necessary for piping heating boilers. Let's consider cases when its installation is necessary:

• IN solid fuel boilers for organizing a small circulation circuit.
• As a bypass for the pump.

A pump is often installed on the bypass pipe. And this is not always necessary. Single-pipe and double-pipe heating system with forced circulation will not be able to work without a pump. Therefore, in order for water to flow in a straight line, a bypass is necessary.

And in a system with natural circulation work efficiency increases. To do this, install a bypass with a check valve in the direct line. In the event of an unexpected power outage, automatic switching to the natural movement of water.

A bypass is often installed in a solid fuel boiler. It allows the heat generator to heat up to 50°C in order to avoid corrosion on the steel walls of the firebox.

Until the coolant heats up to the required temperature, the valve will not allow cold water from the system into the boiler. Then the valve opens and lets cold water through and mixes it with hot water. In this case, condensation will not form on the walls of the firebox, and, therefore, corrosion will not form.

A bypass is also required in the water supply. If you need to repair or replace a heated towel rail in your bathroom. Without a bypass, this will be problematic. In a multi-storey building you will create many inconveniences. Therefore, it is recommended to install a jumper in advance when installing the heater.

Bypass features

Bypasses have some features:

• When installing a bypass, you need to pay attention to the diameter of the unit. It must be smaller than the diameter of the supply pipeline;
• For the bypass device, it is best to use American nuts. They allow you to quickly disassemble the valves and pump in case of any repairs;
• In order to avoid airing in the system, the unit can only be installed horizontally;
• It is necessary to install plugs at the top and bottom of the pipe;
• The knot can be made by hand. To do this, you need to purchase a tee, a piece of pipe and welding machine. But you can also buy ready-made elements and assemble them using threaded contacts;
• It is necessary to install a thermostat or control valve between the bypass and battery inlet holes;
• The bypass should be installed next to the radiator, but away from the riser. The most appropriate place It will be where the temperature is not very high. Also, the service life of the bypass will decrease if it is installed next to a heating boiler;
• A special coupling must be installed on the bypass pipe. This is necessary for its easy removal along the thread during repairs.

If you cannot install the bypass yourself, you can invite a specialist. At correct installation Bypass you will notice a significant benefit.

Via bypass in the heating system modern house mount it all key elements. It's simple engineering solution facilitates maintenance and repair of equipment connected to the main line. It also increases the efficiency and economy of heating, which is not bad at all, isn’t it?

Do you want to add a bypass to your heating system, but don’t know how to do it correctly? We will help you cope with the task - the article discusses the purpose of this element of the heating system and key points its installation.

A bypass, or bypass bypass, is a pipeline that serves to organize the flow of coolant bypassing a certain area heating main, or parallel to it.

Most often, some equipment is installed in this area. One end of the bypass pipe is connected to the inlet pipe, the other to the outlet pipe.

Shut-off valves are installed between the bypass and the inlet of the device being rounded. It allows you to completely redirect the flow of water along alternative path, or regulate the amount of liquid entering the device.

For the opportunity complete shutdown equipment, a tap is installed on the outlet pipe - between the outlet of the device and the bypass.

Image gallery

Since the hydraulic pressure on the side of the outlet pipe is higher than on the side of the inlet pipe, the ball is pressed tightly against the valve seat and completely blocks the lumen of the pipeline.

A bypass is a jumper installed on the thermal route parallel to the main line. This simple detail in the form of a piece of pipe helps solve various problems and is therefore considered important element any scheme. Why a bypass is needed in the heating system of an apartment and a private house is described in detail in our material.

Bypass installation options

Once we have determined what a bypass line is, we will consider the question of why it is needed and where it is installed. Depending on the problem being solved, the element takes the form of a bypass pipeline or a straight section connecting the supply line to the return line.

Reference. English word bypass literally means “bypass”, “bypass”.

There are several options for installing bypasses in heating systems:

1. On radiators of closed and open single-pipe systems.
2. Parallel to the circulation pump operating in a gravity (otherwise known as gravitational) heating network.
3. A jumper between the supply and return, forming a small circulation circuit for heating a solid fuel boiler.
4. In various mixing units.

IN apartment buildings, where heated towel rails are connected to a common hot water supply riser, a bypass line is also used, which operates in a similar way to a radiator line (item 1 of the list). We will explain further why it is needed there.

The pipes of heated towel rails have large diameter and throughput, the jumper is needed only for convenient removal of the coil

The first two options are well known to owners of private houses and apartments. Unfortunately, some owners, who consider themselves major specialists, “improve” bypasses or install jumpers where they interfere normal operation heating systems. We will also consider random and intentional errors.

Single-pipe radiator jumpers

In the majority multi-storey buildings Soviet-built heating is organized using single-pipe vertical risers running through all apartments. The principle of operation of the scheme is to distribute the coolant among the batteries on the 5th-16th floors due to the high flow rate and increased pressure.

For reference. Old cast iron batteries and steel ribbed convectors were distinguished by large diameters of internal channels, whose connection to the riser was designed without any bypasses. We are talking about new generation devices with high heat transfer and lower throughput.

Options for single-pipe heating schemes for multi-storey residential buildings

Please note that the radiators are connected to a single line by both connections, between which a bypass is inserted. The pipe jumper is specially shifted away from the axis of the riser, otherwise the water will not flow into the battery, but will move along a straight path down or up, depending on the direction of flow. Ideally, the circuit works like this:

1. Having reached the fork in the first heating device, the flow of hot coolant is divided approximately in half - one part flows into the radiator, the second rushes into the bypass.
2. Having cooled by 1-2 °C, the first flow is mixed with the bypass flow and returned to the main line. The temperature of the resulting mixture becomes 0.5-1 °C lower than the initial one.
3. The process is repeated in a similar way on the following heating devices. To ensure there is enough heat for all consumers, pumps district heating pump a large amount of coolant through the mains, reducing the temperature difference between the first and last battery.

In private two-story cottage the straight section is placed on the upper batteries

Note. Similar schemes are found in two-story private houses. And although the vertical riser supplies only a couple of radiators, it is advisable to install a bypass on the upper heater, since the performance of a household circulation pump is much lower than that of its industrial “brother”.

If you remove the direct bypass line, the entire volume of water will flow through the heating device and cool by 1-3 °C. Because of big difference temperatures each subsequent apartment will receive significantly less heat. The room with the last radiator will become as cold as a doghouse.

That's why when vertical single-pipe scheme a simple piece of pipe on the battery plays an important role. In two-pipe distributions, hot and cooled coolant flows through different highways, so no bypass is required.

Here the role of the bypass line is played by the distribution pipeline itself

In country houses, the low performance of the circulation pump is compensated by increasing the diameter and bandwidth pipelines. This is done in the horizontal single-pipe system shown in the photo. The bypass is the main line, where approximately 2/3 of the coolant flows, and the third part enters the batteries.

Circulation pump bypass line

In the majority modern systems water heating pump unit crashes directly into the supply or return pipeline, which is described in detail. There is no need to install a bypass in this case:

• if the power goes out and the pump stops, the coolant will still not be able to circulate on its own due to the small diameters of the pipes;
• to remove the pumping unit for the purpose of repair or replacement, it is enough to turn off 2 taps and unscrew two American valves, provided that the unit is assembled correctly;
• since water is unable to move along the lines without being forced, the bypass jumper will not help maintain the operation of the system while the pump is being serviced.

This scheme can operate in forced and gravity mode

The only case when you need to make a bypass branch for the circulation pump is a gravity heating system. Firstly, a unit with connection pipes DN 25-32 cannot be inserted into a Ø50 mm pipe used in the gravity heating network of private homes. Such a narrowing of the diameter will stop any gravity flow.

Secondly, the heat supply must work according to universal scheme. The main mode is forced from the pump; in the event of a power outage, a transition to the natural gravity flow of the coolant due to convection. To organize such heating operation, the pumping unit must be installed on bypass.

There are 2 methods of installing this unit:

1. A ball valve is inserted into the direct line, and the heating pump is brought to the bypass line along with mesh filter– a mud trap and shut-off valves.
2. A ready-made bypass unit with a pumping unit and a check valve is placed in the main gap.

Installation of a pump unit with a shut-off valve on a direct line

In the first option, the transition to gravity mode is done manually. When the power supply stops, one of the household members should go to the boiler room and open big faucet on a straight section. Otherwise, without water circulation, the boiler will stop heating, the building will cool down and you will freeze.

In the second case, after a power outage, the automatic check valve in the closed position while the pump is running. But not everything is as rosy as it seems at first glance:

Hence the conclusion: do not install ready-made automatic bypasses with a valve and pump. It’s better to assemble a unit with a shut-off valve with your own hands. The house will begin to noticeably cool down 30-40 minutes after the shutdown, which is quite enough to open the main highway.

The rubber ball rolls freely inside the chamber and closes the passage under water pressure

Option two: install a bypass unit from individual parts, using a brass check valve with a loose rubber ball not pressed down by a spring. What such an element looks like, look at the photo and video:

Mixing nodes

These elements of heating systems consist of a three-way thermostatic valve and a bypass connecting the return pipeline to the supply. The bottom line is this: the bypass branch helps to collect coolant from two lines in the valve chamber, and at the outlet to obtain water at the required temperature.

The principle of dismounting using a jumper and a 3-way valve is used in various sections of the heating network:

• small circulation circuit of a wood-burning boiler;
• piping a buffer tank or heat accumulator;
• along the heating circuits of a water heated floor.

For reference. The scope of application of mixing units is quite wide. Adjustable lowering of water temperature by stirring is used in units air heating(heaters) and other climate control units.

Scheme with a boiler circuit that protects the heat generator from condensation

The bypass shown in the diagram with a three-way valve, forming a small circulation circuit, protects the solid fuel boiler from the release of condensate during the heating phase. The process algorithm looks like this:

1. When the wood is ignited and the pump is turned on, the valve remains closed on the heating system side. Leaving the heat generator jacket, the water turns into the bypass line and returns to the boiler.
2. As it heats up, the temperature of the looped coolant increases. When it reaches the threshold level of 50-60 °C (depending on the setting), the thermocouple of the valve is activated, gradually opening the flow from the radiators.
3. The more the water in the boiler circuit heats up, the wider the passage for cold coolant from the system opens. Mixing occurs in the valve chamber, but the outlet flow temperature will not fall below the set threshold until the fuel is burned.

B with cast iron heat exchanger The bypass mixing unit plays the role of a safety element. Situation: the heating is working at full capacity, the firewood is blazing, and suddenly the lights go out. If there is no safety net in the form of a UPS or electric generator, and the power supply is restored after 30 minutes, the water in the batteries has time to cool down.

A relief line with a bypass valve is not always found on factory manifolds, but it will extend pump life.

Please note that the boiler will not have time to cool down within half an hour - the firebox is full of heat and firewood. As soon as the pump turns on, cold coolant is pumped into the boiler jacket and the temperature shock cast iron section bursts. Therefore, in this case you cannot do without a bypass.

A similar principle of mixing by means of a jumper and a valve is used in the distribution system. When the temperature in the heating circuits has reached normal (35-45 °C), the 3-way valve closes the supply side of the boiler, and the pump drives the coolant through the bypass along the inner ring.

Note. In case the automatically adjustable circuits close together, the comb is equipped with an unloading bypass. Thanks to it, the pump “spins” the water through two collectors, rather than mixing it inside itself, which reduces the resource of the unit.

The use of a connecting jumper in the buffer tank piping is identical previous versions and is shown in the diagram.

When tying the buffer tank with solid fuel boiler 2 bypasses are used

Installation errors

Some home, or rather, apartment craftsmen when replacing old cast iron radiators on new aluminum ones they deliberately make two stupid mistakes:

• install a ball valve on a straight bypass pipe in order to direct all the coolant into its own battery;
• Having listened to the advice of “smart” people, they assemble a mixing unit with a three-way valve in order to regulate the heat transfer of the heating device.

Let’s immediately make a reservation that such installation in a private house is not considered a mistake: you live there alone and control the heating yourself. In a high-rise building, such actions harm the neighbors, since you unbalance the system and take away large quantity heat. This means that adjacent apartments receive less. How this happens, watch the video:

Instead of further listing the errors, we suggest that you familiarize yourself with the recommendations on how to properly install the bypass yourself:

1. Jumper on battery apartment building- this is a pipe without any shut-off valves and valves. The maximum that is allowed is to reduce the diameter by 1 standard size (riser DN 20 - connector DN 15);
2. If you want to regulate the heat transfer of radiators, please install manual or automatic thermostats. There are special full-bore models for centralized networks.

   IN multi-storey buildings with common risers, it is unacceptable to install fittings on the bypass pipeline

3. If in country house Energy-independent gravitational heating is organized; mount the pump only on the bypass. Gravity flow is not provided - no jumper is needed.
4. At self-assembly mixing units make sure that circulation pump turned out to be on the outside open exit valve Other options don't work.
5. , equipped with a thermal head, operates from remote sensor temperature. Place the latter on the pipe behind the valve, where the mixed coolant exits. Then the element can be guided by its temperature.
   

Point #3 requires clarification. With 3-way valves, one pipe is always open - the one from which the resulting mixture comes out. A pump is installed on the same side. If the unit is placed on any inlet pipe, then further events will follow one of two scenarios: the circulation will stop or the coolant will flow through the bypass, close in the boiler circuit and not get into the radiators.

In conclusion, briefly about DHW

Since we have made all the main conclusions in the course of the description, we will supplement the information picture by installing a bypass on the heated towel rail. This is the only case when a piece of pipe is installed only for ease of maintenance or replacement of the heater. The element has virtually no effect on heat transfer due to the flow speed and pressure in the water supply. The principle of operation is similar to the operation of a bypass on radiators, only here we distribute hot water.