See there’s that return valve which is used to let water into the system when yer pressure drops much below 1. Why does mine keep doing that? I’ve had to do it twice today already.

Any plumbers in today?

it is higher when it is on and hot than when it is cold if not that then it must be leaking/venting somewhere

Yup, if the pressure’s going down, stuff’s coming out somewhere.

Burst a pipe in the cold weather?

are any of the rads cold at the top? Might be worth giving it all a good bleed (which will drop the pressure – make sure you ‘top up’ as you go around) and seeing if it continues to drop.

Expansion vessels knackered. It’s there to compensate for the expansion of the water when it gets hot. If it’s not expanding then the expanded water gets dumped out the overflow pipe. Next time you look at the pressure, particularly if the systems cooled down, it’s way down. Had it happen a couple of times on our boiler and some of our neighbours as well (we all have the same boiler).

Will go for the bleeding option. I dunno about the off/on comparison, it’s been on pretty much constantly! But that also implies that the burst pipe option is less likely. Not seeing any water from a leak, is there a particular bleed order? Should top up be done with boiler off or on?

aahh! Expansion vessel, hmm will look for dumping, though. I’ve not seen the gauge go over 3

I always started at the top of the house and worked my way down.

with a pressurised system I’m not sure it matters but I used to do it with it on and checked the bolier pressure after each rad (or even mid rad if there was a lot of air in it).

mine drops pressure gradually – over 3 weeks or so in the winter, and every couple of months in the summer. Told by a few plumbers (none of whom put the system in) that ‘they all do that’.

Over a day is too fast. The most obvious candidate will be a leaking rad valve. Some of mine occasionally stick so much that when you open the valve, you’re actually opening the threaded bit below it. 11mm spanner sorts it out. To find the leaking one, wrap a piece of kitchen towel round each rad pipe, the wet one is where the leak is 🙂

Does sound like the pressure vessel.

It will need the system part draining to remove any pressure on it and then the pressure vessel pumping back up to its recomended pressure. It might have just lost its charge of air over time or have a vaulty valve but often they have a hole in the diaphram in which case it will need replacing. Sounds like it is time to call a plumber / heating enginner.

Expansion valve. It really is an easy fix and doesn’t need a heating engineer. Just needs your track pump (schraeder valve).

Cheers SkillWill, but the potential to cock up majorly is tooooo scary

had a new pressure vessel in this October after much the same thing. Pressure used to vary enormously from day to day. System died 22nd November during the first snows 🙁 . Very, very cold and after 45 mins one morning when it was -4 trying to start it had enough….. Just spent £2200 on a new boiler last week as the old one was 12 years old… Know a good honest plumber???

Know a good honest plumber???

I do, but he’s not very well.

I hope you’re not referring to me as a plumber

🙂

It said ‘honest’ as well!!

Mine has started doing this also, I too concluded it was probably the expansion vessel as I’m not getting wet anywhere, but I’m also not leaking outside.

I had the same expansion vessel issue on my combi

Tap it with a spanner it should sound hollow if not the bladder could be fugged and the vessel is full of water

Alas it was a drain down job to replace took me about 1 hr including refilling the system in a 4 bed house

Got my vessel from here http://www.heating-parts.co.uk/
cheapest I could find

DO NOT CALL IN BRITISH GAS THEY WILL ONLY TRY TO SELL YOU SOMETHING ELSE OR TELL YOU YOU NEED A NEW BOILER TO BOOST THERE “QUDOS” POINTS

Plastic sandwhich bag over the discharge pipe, a clothes peg usually fits round it and keeps it on, check after a few hours of operation.

If nowt there, you’re loosing it elsewhere. Is it a condensing boiler? If so, it’s possible that the heat exchanger has an internal leak which Is draining through the condensate drain.

Other than that, it’s a leak under the floor or something similar.

Yeah. Ours did this for ages until I got annoyed and opened up the house like a kipper. I eventually found a very slow leak in one of the pipes running under the landing. It was leaking anough to drop water pressure but not enough to ever soak through the ceiling. (Mainly because the only time it leaked was when the heating eas on which dried it out as fast as it leaked)

Is it a condensing boiler?

how would i know?

how would i know?

It’ll break every winter just when you need it.

Then i have one.

What type is it? Make and model.

Vaillant TurboMax

That’s not a condensing boiler. Try the bag over the discharge. After that. It’s a look at the boiler, lift some floor boards job You could try adding leak sealer to the system and giving it a few weeks

Heard an ‘amusing’ plumber story yesterday…

My business partner’s boiler was on the blink so he took the afternoon off to wait at home whilst the plumber fixed it. The plumber rang half way through the afternoon to say he couldn’t make it and he would ring back later to re-arrange.

So my business partner calls another plumber who comes straight out. An hour into the job the other bloke appears on his doorstep so he is sent away (after delivering a stream of abuse about his wasted time).

The plumber that did the work goes back to his van to find a brick through a window!!!

My business partner rang up the other guy who delivers another stream of abuse then says ‘well it wasn’t me – you can’t prove it was anyway’.

:-O

just tell the plumber who did it – had similiar with a carpet fitter who kept upping the price – despite the aggrement-then told me to f off in my own house with my 2 year old stood nect to me when I told him to leave a sI would not pay – he had done no work at this point. My son left the room the door got shut and a frank exchange of ideas about customer respect ensued.

BG service peeps get a cash bonus if they flog you a new boiler, so they are incentivised to lie to you….

Cheers Paulo, Of course you’re not a plumber, got a white collar last i heard. 🙂

Back on topic, my boiler used to do the pressure fluctuation thing a lot. Sometimes keeping pressure for a week or more, other times dumping it right down to 0BARG in the space of a day.

I thought it was probably a pressure vessel / diaphragm fault, as I had no leaks anywhere. Put it on my round tuit list.

Doing a spot of kitchen renovation, I removed a radiator. During the removal, it appeared that the feed pipe to the rad was a bit ropey, and the connection valve onto the rad was seized, which was going to rip the pipe out. Drained down, replaced the rad valve and a bit of pipe – and noticed a green staining on the pipework. “Hmmm… ” I thought.

Since re-assembling and refilling etc, the pressure has been steady for a month or so now….

So, tiny weep on a fitting can lead to all sorts of pressure gauge fluctuations, and can be a right pain to find.

We just had the expansion vessle replaced and it solved the problem for us.

CharlieMungus – Member
Cheers Paulo, Of course you’re not a plumber, got a white collar last i heard.

I prefer to call it the darkside. Still wasn’t a plumber though 🙂

I know, I know, you were erm… er… a fitter!

😛

Mine did this last winter. Turned out it was a leaking heat exchanger within the boiler.