# Heating: refill with water - heating filling

## Which minimum pressure is required?

Sense of proper pressure of the heating system is the guarantee that the water really reaches the top of the heating. Therefore, it is important to know the difference in height between the pressure gauge and the height of the heater. This height in meters is multiplied by the factor 0.1 and gives the minimum pressurethe water reaches in an open system.

If necessary, this value can also be determined without known height. For this purpose, the heating circuit is opened at the highest point until no more water escapes. The pressure displayed now indicates the minimum pressure that will be generated when the heater is filled to the top with water. Theoretically, this determined pressure would be sufficient.

In a house with three floors of 3 m each, the pressure would be around 0.6 bar. The value is 2 m in the first floor, as the manometer is probably not on the ground, but is mounted at a height of about 1 m. The second floor is counted continuously with 3 m, since the water column is consistently up to the third floor, in which the top of the heating or the highest point is located in about 1 m ceiling. Together, this results in 6 m height difference - the value can of course vary according to the circumstances. However, the calculation example shows that a significantly higher water pressure makes little sense and unnecessarily stresses the heating system.

Note: Height difference between the manometer and the highest point of the heating multiplied by 0.1 = required minimum pressure.

## Why even a water pressure in the heating system?

A heater needs to heat transfer water, which is heated and pumped through the heating system. If this water is missing, the heat can not be transported and released in the radiator. But why does the heating system need an operating pressure for this?

Actually, a heating system does not require pressure, this is automatically determined by the weight of the water and the height of the entire heating system - between pressure gauge and highest point of heating. One meter of difference in height creates a pressure of 0.1 bar. In a house with a total line height of 6 m, this results in a pressure of 0.6 bar. If this is achieved, it is guaranteed that the water column is at a height of 6 m. The example shows that there are no lump sums for every heating system. Although a value of 1.5 bar is often recommended, this is only an average that works as well as possible in single-family homes.

## What role does the expansion tank play?

Water, like many other substances, expands when heated. However, since water can not be compressed, this expansion would lead to an enormous overpressure, which can damage the heating system. The expansion tank is able to compensate the overpressure.

Expansion tanks consist of an airtight metal container in which there is a rubber bubble, which fills in the expansion of the water. The air cushion between the housing and rubber bladder provides space to accommodate the expansion of the bladder. A pre-set air pressure in the housing also makes it possible to keep the water pressure in the heating circuit constant. If, for example, the air pressure in the tank is 1.5 bar, any opposite water pressure of more than 1.5 bar is absorbed and the pressure in the heating circuit is kept constant at 1.5 bar.

But how high should the preset pressure in the expansion tank be? In the example it was shown how the minimum pressure of the heating system can be calculated. Every meter of difference in height in the heating system requires 0.1 bar. For safety, 0.3 bar is added to the required minimum pressure. If the minimum pressure is, for example, 0.6 bar, this results in a required air pressure in the expansion vessel of 0.9 bar. The pressure control in the expansion tank must be carried out with open, pressureless heating system!

Many pressure gauges already have green and red markings, which indicate a meaningful operating pressure. This is usually between 1 and 1.5 bar, which can certainly be used for a lower required minimum pressure. Nevertheless, caution is required. The larger the heating system is and the more water there is in the system, the more this water expands. If the preset operating pressure is too high, the expansion tank can no longer compensate for the overpressure and the pressure in the heating system rises.

## Prepare heating water in accordance with VDI Guideline 2035

Who fills his heater with tap water, must - depending on water hardness - in the worst case expect functional damage. The water contained Minerals, such as calcium and magnesium, lead to lime deposits in the pipes and radiators, As a result, the energy is no longer transmitted unhindered and the heater is not sufficiently warm. In addition, the sulfate and chloride contained in the tap water can lead to further malfunctions - in the worst case, failure of the heater. In addition, heating water that does not comply with the VDI directive endangers the guarantee and warranty claims.

To prevent damage, limit values ​​for the pH value and the water hardness of the heating water are valid according to the VDI guideline 2035. If these are exceeded by the normal tap water, a water treatment is unavoidable. For this purpose, manufacturers offer various solutions, eg. B. a system treatment plant that processes the heating water in the existing water cycle without interrupting the operation. In addition, demineralization equipment and automatic heating filling stations are available.

## Heating filling according to EN1717

Since 1 August 2011, the European standard DIN EN 1717 replaces the previously valid DIN 1998, Part 4. The new ordinance stipulates that in the case of a hose connection between the heating filler neck and the water tap (or another fitting carrying water) System separator must be used. This system separator prevents heating water from flowing back after filling and / or being sucked back, as well as causing germs and other harmful substances to enter the drinking water. As a result, the permitted by the old DIN 1988, Part 4 short-term connection is no longer permitted.

In the case of system separators, a distinction is made between class BA and CA: System separators BA belong to group B according to EN1717 and are equipped with a chamber system with controllable pressure zones, which prevent the return of the heating water into the drinking water network. They are used for protection up to and including liquid category 4, ie heating water with ingredients.

On the other hand, system separators CA are assigned to group C. They also have three pressure zones, but may only be used for filling up to and including liquid category 3, ie heating water without ingredients.

Installation of the system separator:

Before the system separator BA or CA is put into operation, the pipe should be thoroughly rinsed. Subsequently, the separation module is installed horizontally, taking into account the flow direction. In both cases, the installation should be stress-free. In addition, the installation instructions of the manufacturer must be observed.

## Refill heating water according to DIN 1988, part 4

1. Before filling the heating system with water you should use the Switch off the pump and open all valves of the connected heaters completely.

2. To refill the missing water in the heating system, connect a normal supply hose to the connection piece of the heating system and to a water connection. Do not fully tighten the connection on the filler neckso that contained air can escape.

3. Carefully turn on the water tap at the other end of the hose and allow the water to run until the hose is completely filled with water and free of air. A bucket or bowl catches the leaking water on the loose filler neck.

4. Now firmly connect the hose to the heating system and open the valve at the tap so that the connection hose is under pressure. Under close observation of the manometer can now open the valve on the filler neck and fill the heating system become.

5. The indicated water pressure increases until the pre-set air pressure in the expansion tank is reached. More water can not be replenished. Since the expansion vessel would equalize further pressure, and thus no longer indicate when too much water is filled, exactly the point must be adjusted, where the pointer of the pressure gauge stops. Optionally, the expansion vessel can also be separated with a ball valve. Also in this case, no more water should be filled until the set air pressure at the expansion vessel is reached. Too high water pressure would be displayed by the manometer in this case.

6. When the required operating pressure has been reached and, if necessary, the expansion vessel has been reopened, the heating system can be put into operation. Leave this all thermostatic valves open and pour the water through the radiators for a few minutes, It is not necessary to heat the water while doing so.

7. Due to the short operation all the water was set in motion and possibly contained air should have collected in the radiators. Now it is important Check and vent all radiators, If some air or water escapes, the pressure on the manometer must be checked and, if necessary, water should be replenished.

tip: After filling the heating system, it may be necessary to bleed the heating. Newly filled heating water will leave you feeling very strong during the first days. This creates air cushions and the heating water starts to churn. Check the operating pressure again after a few days.

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