Low pressure in combi boiler.

[acrabadabra]

Can anyone explain why my boilers pressure keeps falling?

I can fix it by repressurising it but just wondering if I should get a plumber in.

Have you bled any of the radiators recently? That will send the pressure down. Otherwise, I think they just lose pressure over time.

Small leak in one of the radiators or pipes? Radiators can get pinhole leaks. Check thoroughly, also boiler itself might have a leak inside, ours did, left it too long and needed a whole new boiler.....

Leak. If you can't see it, could be in or under the floor. Start by looking at the pressure relief pipe on the outside of the house where it comes the wall behind the boiler. Look around and under all radiators and pipes.

Ours used to lose pressure because one of the valves on the living room radiator has a small seeping leak. Now it loses pressure because there is an ENORMOUS leak in the new pipework ;)

How long does it take it to lose pressure? When we had a sort of seeping leak, it took ours about two weeks to get below the line. When we had the dripping leak, it took about two days.

Initially it took a few weeks but I was shown how to repressurise it and bleed the rads. After that it took about 2 days.

Is it possible that I've just not tightened the key on the rads enough? I will also check for any leaks though haven't noticed anything.

I first noticed problems after I had a washing machine fitted. I guess it could be around there.

They should teach this stuff at school.

Your washing machine shouldn't cause it, unless they fitted it to the central heating pipes, which would be very very wrong.

To my knowledge (trembling in fear of PJ) the hot water (to which your machine is probably but not necessarily connected depending on whether it is cold or mixed fill) is on a completely different circuit to your central heating circuit, which is what is pressurised in the boiler. Your central heating circuit just recycles waters, heating it up in the boiler and circulating around your radiators. Your hot water flows frm the mains, through the boiler where it is heated (but not the pressurised tank bit) and into the hot water taps. So depressurising is likely to be a leak in the central heating pipe work (I've had one of those) or a leaky valve/radiator. So if you haven't tightened the key on the rads (don't overtighten though) enough, it could be that, or a valve or joint is just spitting a bit. You could check around the washing machine to see if a pipe has been knocked, causing it to leak. Is it a new boiler? sometimes new boilers on old systems can cause problems in old solder joints because of the power flushing/higher pressure. Look in your airing cupboard if you have one, sometimes there's a lot of pipe work in there. My leaks were behind the dishwasher, at the bottom of the airing cupboard and then inside the boxed in pipes (that was the worst one, but made itself known quite quickly!).

It's frustrating not knowing itsn't it! I have an elderly copy of the Reader's Digest Guide to DIY which has been an absolute boon to me over the years (used it to replace the pump on my conventional system for example). I agree that this sort of thing should be taught in schools. Or at least a sort of 'how to be an informed householder' course at night school!

Think this happened to my friend and it was because of a broken 'heat exchange' part in boiler.

Thanks for the ideas. Have had a cursory glance round the rads and can't see anything obvious. I'll get a better look tomorrow.

If I can get a plumber to call me back I will get an expert in next week.

Have you looked yet at the pressure relief pipe that goes through the wall behind the boiler?

Boilers losing pressure is the most common problem I deal with as a gas engineer. 100% check the pressure relief pipe as mentioned by PJ. Thats by far the most common place to find a leak. Its usually on the outside wall just under where the flue comes out. Even if it appears not to be leaking, wipe your finger around the end of the pipe. Depending on the volume of your central heating system evn a tiny leak can drop the pressure over the course of a couple of days.

Next check your radiators and especially the valves that connect the pipes with the radiators. These can leak slightly if they have been knocked by the hoover. Again it can be a seemingly insignificant amount of water.

The third most common point of failure is inside the boiler. Especially a combi (lots of plastic parts and washers that can degrade very quickly).

Which combi do you have? Certain models have parts which always leak.