Boiler loses pressure when heating goes on All aspects of plumbing questions and answers, help, tips and information

[RB101101]

Hi

I have a Worcester 24i boiler. When the heating goes on, it loses pressure and needs to be repressurised using the filling loop.

Someone's come out to have a look at it and has checked it over and apparently the boiler itself is fine but they think that there must be a little leak in the pipes somewhere.

He put a fluid into the system which is supposed to plug any leaks and the heating needed to go on for a day or two to allow this to circulate. However, no joy with that, it's still losing pressure.

The next step looks to be taking the floorboards up to look for the leak.

I wanted to find out if there are any ways to detect leaks without taking floorboards up or is this not the sort of kit that's generally used by heating engineers? I'm keen to avoid having to take floorboards up if possible but it sounds as if this might be the only way?

Cheers

Ruth

[stoneyboy]

Hi rb101101,
If a system has a leak this would normally show by falling pressure when the system is off. Suggest you start by looking for leaks in the boiler itself also, does water run out of the pressure relief pipe on start up?
Regards S

[RB101101]

Hi, and thank you.

When the boiler only gets used for hot water, the pressure drops but very very slowly. So I need to re-pressurise it let's say, once every couple of weeks.

When the heating gets switched on the pressure will rise and remain constant whilst the heating is on but then as soon as the heating is switched off, the pressure starts to drop back past the level it started off with. So I can start at 1.5 when it's off, it'll rise to 2 when the heating is on and then when it's off, it'll drop down lower than 1.5. So each time it starts at a lower point and then I have to re-pressurise it again. Hope that makes sense.

When the guy came along, he checked the pipe outside and there was a water leak. He replaced a valve which he showed me was worn and corroded.

However, that didn't solve the problem and so the next step was to put the fluid into the system that should seal any leaks. But that didn't work either.

I will go and take a look outside tomorrow however to check if that exterior pipe is wet or dry.

Hope all that makes sense!

[stoneyboy]

Hi rb101101,
I would suspect that your pressure vessel has failed so there is no compensation for system pressure changes.
Your system pressure should be set 0.5 to 1.5 bar and if the pressure rises much above this the pressure relief valve will operate.
Regards S

[RB101101]

Aha, OK - interesting. When the heating was switched on to flush the fluid to seal any leaks around the system, the pressure was dead-in consistent at 2. After it was switched off it started dropping and now it sits at just below 1. This will be fine for a couple of weeks if I only use hot water, after which time it'll drop a little further. However if I switch my heating on it'll rise a bit and then drop further quickly when I switch it off.

I'll go and take a look outside to see if there's any water coming from the boiler pipe both when the heating is off and when it's on. Might provide some more clues if it's wet maybe?

TBH, any work on the boiler is going to be preferable to having to take floorboards up to look for a leak.

Thanks for your help with this, very much appreciated.

[RB101101]

Hmmm....the pipe outside is dripping so thanks for your help with this. I've got someone to come and take a look at it. Hopefully it's a boiler issue which won't need all the floorboards taking up.

Thanks once again!

[stoneyboy]

Hi rb101101,
Thanks for the update, the pressure vessel is the most likely culprit.
Regards S

[RB101101]

Great - hopefully I'll get the thing fixed before it starts snowing :)