A filling loop left open can cause the pressure to go too high. Follow these steps to fix the problems.
What is a filling loop?
A filling loop is used to add water to a central heating system. Sealed central heating systems have to be filled with mains water to about 1 bar of pressure. A standard filling loop comes in 3 parts:
- Mains cold isolation valve with non return valve.
- Central heating isolation valve
- A connecting hose.
Why is my pressure rising
Water is passing from the mains cold valve to the boiler through the heating system valve. This is through the filling loop pipe.
Correct use of a filling loop
Close the valves on the filling loop after use. The metal braided filling loop removed and the valves capped. The majority of people don’t do follow this clumsy procedure. This means there is a chance that the valves can be opened accidentally or leak. This causes the pressure to go too high and makes the metal pipe near the boiler overflow.
My filling loop was left open – what to do?
The first step is to turn the taps so they are in the off position. If its a round tap turn it clockwise. If it has a lever turn it so that is not in line with the valve. If it has been accidentally turned on you will hear the water flowing. You will hear the flow stop when you turn the valve to the correct position.
Can you can still hear the water flowing even when the valve is in the closed position? Go to our guide on a passing filling loop.
Filling loop positions
The filling loop below is open. Even if the black handle of the tap is slightly turned water can flow. You can normally hear the sound of water moving through the pipework.
The filling loop below is closed. The black handle is across the pipe so it is closed. You shouldn’t hear any water flowing in the pipe.
It doesn’t need to be as pronounced as this to cause the pressure to go up. Even slightly open is enough to make the pressure rise..
How to fix a filling loop left open
To fix this you need to turn both valves (or one if you only have one) off. When you turn both valves off you will hear the water stop flowing. This should make the metal pipe outside stop overflowing and the pressure should stop rising. (This takes a few minutes).
In general, if the handle of the valve is in line with the body of the valve it is open. If the handle is across the body of the valve the valve is closed. For filling loops with a circular handle turn it clockwise to turn off. (For more info follow this link).
How to reduce the pressure in your boiler
You can reduce the pressure in your boiler by either bleeding a radiator or opening a drain valve. This can either near the boiler or on a radiator. If you aren’t sure get help.
The safest way is to bleed a radiator. Reducing the pressure this way is very slow. But it is much more reliable and less likely to cause trouble than opening drain valves.
Place a towel or tray under the radiator and slowly let the pressure out.
Next steps
The metal pipe outside is linked to a safety valve inside the boiler. This valve is shut for many years. After opening they tend to not seal up. (some do but most don’t)
The metal overflow pipe should only overflow if the pressure is above 3. So when the pressure goes back down below 3 the water should stop flowing outside.
If it doesn’t reseal then you need a new safety valve. This is a job for a gas safe engineer, not DIY. Each boiler manufacturer has a range of safety valves for their boilers. The aren’t cross compatible with each other.
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