British Gas can’t solve this:

Our Boiler, when the heating is on ALL the time maintains 1 bar of pressure, works fine. Turn it off, all the pressure drains away. Top it up over 1 bar and put it on, pressure slowly lowers and then maintains 1 bar. Top it up and leave it off, all the pressure drains away again.

The Pressure Release Valve (PRV) has been replaced twice, to no avail. They are telling me I need a new boiler, but frankly I don’t believe them. Its a Potterton Puma 80e btw.

Obviously its costing a fortune as we can’t used the boiler on “Timed”

?

P.S. If we DO need a new one, anyone fancy the job at Singletrack members rates? 😉

similar experience, pressure correct but boiler used to vent on start up – nice every morning, not quite once a week or so – a potternewton but not that model

eventually an engineer produced something that looked like a bike pump and repressurised the think it is called equalising cylinder, 5minute job

worked ok now for 12months, previously engineers (BG) told me i’d been messing round with pressure too much and all my fault

Similar-ish experience. Potterton boiler now long gone but intermittent dumping (my term) through the release valve (it should be obvious as hell to you that its dumping outside – big smelly puddle).

Ours was under a BG maintenance contract and eventually they fitted a biggish red tank near the boiler – looked like a large fire extinguisher – that the hot feed went into and straight out of the other side. Apparently there was a diaphram in there – hot water on one side – air on the other.

You can tell I’m an expert eh!

lol we are having boiler issues too….. but according to the forums people are sick n tired of the so called experts they call themselves…
anyway we rang the Vokera boiler people cos thats the make of our boiler and they have their own people to fix boilers but its alot of money and its a fixed rate you pay plus a service….just what i needed b4 xmas is the boiler to b on the blink….our boilers water neva gets hot enuff and runs hot then cold all the time….soddin nuisance when you want a nice relaxing bath too much cold water it spews out…been like this for ages…. our boiler is 13 year old hope they can fix it…it probable something and nothing yet we still pay the fixed charge for whatever they change on it….. cud be 50 quids worth of damage or they could fix it for 20 quid yet we have to pay a massive fixed amount of money up front….just incase it costs them x amount of money to fix it…
anyway if you are having pressure problems : it usually means you,ve got a leak somewhere on one of your radiators…

Sometimes when the system is hot things that leak stop leaking (cos of expansion in joints n stuff) when its cold they open up and the water seeps away. Could be a possible explanation, have a good look around the system when its cold.

Hmmm.

looked around the rads, nothing under the boiler where the inlet/outlet is. BG man (x2) says nothing is exiting outside. Antigee – two visits under the maintenance plan and what you described has been checked / pumped both times.

It must be going somewhere…..

If you have the time, see if you can isolate sections of the CH system and see whether the pressure drop reoccurs.

eventually they fitted a biggish red tank near the boiler

That’s an expansion vessel. Pressurised air cavity on one side of a rubber diaphragm, hot water circuit on the other – the diaphragm expands into the air cavity as the water heats and expands.
Im surprised it needed “adding” to a system….

Stoner – I dont know. They came and fettled repeatedly for ages – eventually this red vessel got fitted – problem sorted. Lasted a few years.

Afterwards – a fan or something major went – new boiler went in – red vessel was removed – never had a drop in pressure in the last few years with the same radiator / pipes etc.

You can tell by now I am a real expert, eh?

#Edit – just to add – the indication for us (as experts) of the blow off problem was the rotten coppery/irony smell outside. The vent exited high up – ran down a wall – stunk – and IIRC – left a greeney residue.

I feel your pain. Boiler stuff is horrible and more often that not you have to pay for the privilege of having an ‘engineer’ guess and then guess again. There are good ones but they are usually way over booked.

I would be surprised if it was the PRV as you would usually see it leaking. Do you have the possibility of isolating any of the circuits with shut off valves to see if you can narrow down where any leak might be. So, for example, pressurise the system and then close all the circuits that you can (with the boiler OFF obviously). If the pressure doesn’t fall at the normal rate then try opening them one at a time.

We had a boiler with a leak inside once so there was no water to find – it just evaporated. Isolating the boiler would have found this one for us

Just had exactly the same issue. Turns out a pipe to the expansion vessel was blocked so when the heating system warmed up it couldn’t expand so water vented outside and then when it went off and cooled down the pressure in the system was too low for the boiler to fire up in the morning. Works fine now the pipe’s clear.

You can check if your system is venring water by tying a plastic bag round the end of the vent pipe outside.

you will have a pressure vessel inside the boiler which is filled via a schrader valve (same as car valve)with a removable core when the seal fails the tank leaks air,the 1 bar it goes down is probably air differential .Replace with a new core and repressurise the system,It is actually a common problem and really should be a cheap fix but a lot of so called experts seem to find/sort it and always seem to find costly remedys.Well worth a try I know a few people who’ve been talked into secondry expansion vessels when it’s been no more than a lealing core in the valve.Hope this may help.

On the Puma the Pressure vessel is at the back of the boiler, at the top. Over time the air on one side is replaced with water. It needs equallising you can either over pressure the air side (I wouldn’t) or it would be best to drain the vessel.

Take off the case and find it. Shut all valves and drain all water from expansion vessel. Refill and repressurize using a bike pump.

Or replace it with one further down the line.

Or replace it with one further down the line.

aha. the “adding” of a pressure vessel to a system makes sense now – a cop out 😉

Im guessing that the integrated vessel in the boiler will also only manage to support a maximum volume of system wouldnt it, given the limited space inside the boiler case.

i had similar problem a while back,turns out it was a minute leak on one of the pipes but the drip was so small i only found it after the water had slowly dripped down and it eventually came through the floor-ceiling and i walked on a wee damp patch on the stairs carpet

I’m Wfh today so am experimenting. Boilers been off for a few hours, pressure currently stabilise in the red zone BUT interestingly not right at the stop. Just topped it up – I’m going to give it another couple of hours, leave it cold and see if it drains without the boiler on.

The pressure stuff above makes sense, but the BG guys did at least attach a pump to it and pump it up.

You have a water leak. It’s that simple.

Thanks Mods for moving it the correct area of the forum, and apologies.

Now we are getting somewhere. I followed the suggestion of tying a plastic bag to the pressure outlest / overflow pipe to see if any water was collected. So far today then:

1, Heating on at 1 bar pressure. Turn heating off, pressure falls to red zone.

2. Heating still of, top up system to 1.5 bar. Left it for an hour or so – no movement, no water in the bag.

3. Heating now on, rose to 2.5 bar, currently back to 2 bar, and the bag has about a mugful of water in it.

Thoughts from the experts? Sounds like I have the same issue as Pistola?

It should be easy to detect a perforated pressure vessel. Find the shraeder valve and let a little air out. If you get water it needs replacing. Replacement can be a ‘replacement’ which might be expensive to buy and expensive in labour, especially if it’s tucked in the back of your boiler. A separate vessel will be just as effective plus potentially a lot cheaper.

Doh! Double post.

seems pretty symptomatic of an expansion vessel failure.

Unfortunately you’re not allowed to fit one in the CH circuit yourself…but that’s what Id do (and Im not qualified to either 😈 ), with a new tun dish and outlet 😉

about £100.

You may also just have a leaky valve on the pressure vessel. If you press the valve and get nothing then it may just need a top up with air and a new valve core.

Unfortunately you’re not allowed to fit one in the CH circuit yourself

Since when? Seriously is this disallowed now? I did one in my house a couple of years back to resolve this exact issue.

When your “experts” checked the expansion vessel pressure with a pump, did they first drain the system down, or at least bleed off all the pressure before and during the pumping of air into the expansion vessel. The syptoms are dead typical of a lack of air volume in the vessel, but if they tryed pumping it up to the manufacturers recomended pressure, without draining the water out of it first, there just pissing in the wind. You could achive the same air pressure and still be 90% full of water unless they drain down properly.

Sorry, Im being a div.
Of course this is a Combi boiler installation, not an unvented system (which is where you;d normally find an external expansion vessel), so I guess the regs that apply to quals for unvented dont apply.

Ah, I didn’t realise there were restrictions on vented systems either.

OP, tbh your first mistake was involving BG. Do that check on the existing valve, there shouldn’t be any water at all. If you don’t feel up to fixing it yourself get an independent in and ask BG for a refund. I wouldn’t expect it to cost much more than a couple of hundred quid to get someone in to fit a new vessel.

gingerss – Member

OP, tbh your first mistake was involving BG.

Lol. Indeed – but we have one of those maintenance plans. Its a bit like going to Halfrauds, they never really seem to be experts and you end up telling them the issue yourself.

On a nearly 10yo Boiler though we’ve saved a fortune every year having bits replaced under the contract for effectively £240 per annum, for a bit of inconvience. At least now its not -5 like it was last year when the pump went.

Right, its worse. Another BG mans been back, I told him a condensed version of the above, he’s tested the explansion valve – no water – and ascertained that the pipe from the PRV to the expansion vessel is blocked.

Unfortunately it can’t be removed without removing the boiler completely, as the boiler is less than 300mm from the ceiling (he showed me the manufacturs detail on the website regarding this).

So he recommends

a) An external expansion vessel & MagnaBooster – £275 fitted in our airing cupboard
and/or
aa) A powerflush to get rid of 12 years of sludge – £825 including a)

b) New boiler (ours is 12yo).

Sigh…..

OK, So we have established your pressure vessel has lost its air cushion..hence the safety valve running. Could just be a case of pumping it up to correct pressure, job done.
It could be the diaphragm has perforated or failed in some way. Easiest way around that is fit another vessel somewhere else in the system, Not too difficult but locate near a drain or outside wall to run expansion into.
On the other hand you could have a leak AND a faulty vessel but that’s highly unlikely.

Buy a 8 ltr expansion vessel. Temporarily fit it anywhere you can. If it solves the problem either re-pressurise the one on the boiler or fit the other one permanently.
Lastly, a vessel cant be too big but it can be too small (Capacity) so.. if you buy one and re-press the original leave them both in line.

£275 isnt too bad. In my post above the parts (excl copper) is about £100 and would take half a day to do so that’s kind of BG rates I guess.

If there’s room in the cupboard, Id go for the 8 litre expansion vessel unless your boiler is still under warranty.

Just read the last post.

Magnaboost will not do anything as the scale etc is already there, its a prevention aid. WASTE OF MONEY NOW.

Power Flush wont work either. The pipe in question has no flow of water (its a dead-end) so no amount of ‘in Situ’ flushing will unblock it. WASTE OF MONEY.

A new Boiler would be the answer but costly. If you have spare cash a new boiler is a good option innthe long run.
However I suggest either fit or get someone to fit a new vessel (£50 + Fitting Tops).
Put some form of inhibitor in the sytem once the its all fixed (£15). It will in time lift the solids in the sytem into suspension, drain out and re-fill with fresh water.

Been through exactly the same thing myself over the last few weeks. You don’t need a big leak in the system for the pressure to drop that much. If your overflow is not pissing out water you’re more than likely have a leak somewhere in the system. I decided to crawl under the house to double check all the CH piping, and found a tiny damp patch below a 90 degree connector. Looked fairly inocuous but I thought I’d give it a Quick tighten with the molegrips. Seems to have done the trick though and the boiler is now maintaining pressure.

When I did it the whole job took about 2 hours, including draining etc., and about £60 in parts. The new filling loop in Stoner’s pick shouldn’t be necessary unless you have some weird setup on your boiler.