boiler problem, help with diagnosis

silvercar

Combi boiler (potterton).

When the heating comes on, the pressure gauge increases until it reaches the 3 point at which point it gradually starts to fall, taking a few hours to get back to 1, it then continues to fall until it is at about 0.3.

I think that at the 3 point a safety valve is triggered to release the pressure and this is causing the fall in the pressure.

I'm sure I've had this problem before, but knowing what it is would help.

butaneboy

You have a problem with your expansion vessel, it needs recharging. Could be done diy if you're confident

EliteHeat

This thread might help.

silvercar

EliteHeat wrote: »

This thread might help.

It helped, in that I know I couldn't fix it myself.

EliteHeat

If you can't re-pressurise the expansion vessel, could you not half empty a radiator temporarily? it's cold now

silvercar

EliteHeat wrote: »

If you can't re-pressurise the expansion vessel, could you not half empty a radiator temporarily? it's cold now

The heating is actually working. It comes on but the pressure goes up to 3 and then slowly drops down, the heating is working throughout as is the hot water.

I just realise that it isn't healthy for the boiler to over pressurise itself and use the safety valve to release the excess. Also I am topping up once a day to bring the pressure up from 0.7 to about 1.3 which is not ideal.

EliteHeat

An expansion vessel works on the principle that air can be compressed by the increased volume that the system water occupies as it heats up. If there is zero pressure in the dry side of the vessel or the diaphragm has ruptured, then the pressure will increase since water can not be compressed.

If a radiator was partially emptied then you would have a pocket of air at the top of the rad, this would act as a temporary expansion vessel, and as most rads are tested to 10 bar of pressure, is perfectly safe to do.

This would prevent the pressure rising to the point where the pressure relief valve operates, which is the situation you have at the moment.

hth.

ariba10

We had the same problem with a boiler and cured it by doing as already suggested.

Putting air into the expansion vessel with a car tyre foot pump

silvercar

This would prevent the pressure rising to the point where the pressure relief valve operates, which is the situation you have at the moment.

But does it matter that the PRV operates? Given that (a) the heating is working and (b) someone will be out to fix it in a few days.