fixmyplumbing

Last update: 24 Oct 2023

A filling loop left open can cause the pressure to go too high. Follow these steps to fix the problems. The filling loop is used to fill water pressure into your boiler and central heating system. It should only be used if the pressure has dropped and should be turned off when you are done.

Why is my pressure rising

After use the valves on the filling loop should be closed, the metal braided filling loop removed and the valves capped.  The majority of people don’t do this so there is always a chance that the valves can be opened accidentally or be faulty.  This can allow too much pressure to develop in the system which may cause the metal pipe near the boiler to 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 and at 90 degrees with the body of the valve.  If it has been accidentally turned on you will hear the water flowing and hear the flow stop when you turn the valve to the correct position.

If 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 be able to 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.

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.

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 either near the boiler or on a radiator.

The safest way is to bleed a radiator. Reducing the pressure this way is very slow but is much more reliable and less likely to cause trouble than opening drain valves.

Next steps

The metal pipe outside is linked to a safety valve inside the boiler. As this valve is shut for many years they tend to not seal up after they have been opened by the excess pressure. (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 then you might need a new safety valve as they are notorious for not resealing after they have opened. This is a job for a gas safe engineer, not DIY.