[Closed] new boiler losing pressure

putting a new boiler on an old system can be a bollocks.

i had a number of small leaks that didnt show up to the naked eye when i went from a gravity fed to pressured system.

adding some uv dye to the system and checking every connection with a uv light soon showed up some poorly soldered joints in the old pipework.....

Yes, you'll be surprised just how small a leak can be and still result in frequent loss of pressure.

We spent an entire winter losing pressure every couple of days, it wasn't until the heating was turned off for an extended length of time that we discovered a tiny leak from an upstairs radiator. Whist the heating was on it was evaporating away so no evidence of the leak.

As trail rat said, sounds like leaky pipework, air in the system would result in cold radiators but once at a stable pressure would stay that way. If the radiator you mention is always cold try bleeding it first to eliminate air in it and if its still cold then the leak is probably somewhere at its inlet feed, if it was at the outlet then the radiator would heat but the system would still lose pressure somewhere after it. Could be the leak is under the ground floor but directly above the bare ground so a leak will go unnoticed as its just draining to the ground and not to a wall or floor etc..

The pressure vessel is charged isn't it?

Bleed your radiators after topping the water up in the system.

If you have a lot of air the system it will make the leak appear much worse.

If you are topping up the system to the green section on the pressure gauge and there is air in there, all you are doing is compressing the air.

Top up, bleed and the pressure will drop again. Repeat until no air comes out of any of the radiators. I don't thin it matters much what order you do it in. Just keep bleeding until all the air is gone.

You will find that you may only have to top the system up every couple of months if it's a small leak.

Leak in hot water tank?

If the above fails chuck a can of this into the system:
http://www.screwfix.com/p/fernox-f4-express-leak-sealer-265ml/61837

Fixed the problem with a tiny leak I couldn't track down - been over a year now and pressure not budged from 1 bar.

mmmmmmmmm voided warrenties ahoy.....

7 or 8 times a day sounds a lot :(. Does it still leak at the same rate with the boiler off?

The pressure vessel is charged isn't it?

just had a mate over who's a plumber, said hed give it a quick look. hes found out that the blow-off pipe is leaking substantially to outside. he said thats a boiler problem and shouldnt be happening, and yes, its the pressure vessel thats filling with water or something?

ill get on to Ideal on monday, but he says theyll probably try and blame the plumber. to me tho it sounds like a cast-iron boiler issue.

thanks for the help

Might want to make sure the drain valve is closed of course....

Just asked my mate that, he says you'd have to get inside the boiler to check, but still thinks it's the pressure vessel cos of the pressure rise. (It went up to nearly 3 bar at one point)

mmmmmmmmm voided warrenties ahoy.....

Good point, my boiler is well out of warranty.

The reason I mentioned it is ours failed after a year. Theres a bladder inside a tank. The bladder contains air at a certain pressure, when the water in the system expands the air compresses. If there is no air in it the excess pressure is relieved by dumping water outside. It's a simple job to pump up, there's a schreader valve on the vessel. However it water comes out when you press the pin in the valve the bladder has failed. I'm not sure whether a new boiler would ship with the vessel pressurised. It doesn't takemuch though, about 15 psi I think mine is. However it needs doing with no pressure in the boiler. I used a shock pump to pump mine up which was a bit overkill pressure wise.

...and check the valvecore is in properly 🙂

Did the same with all the suggestions and found a part on the boiler needed replacing as it had become clogged.

If it needs topping up 7 - 8 times a day its not a small leak. Things to check.

You will have a small copper pipe outside pressure relief pipe. Check that this is dry when running and when turned off.

Another thing you can do is top up the boiler to the correct pressure. Turn it off and then turn the 2 isolation valves off at either side of the boiler. Do this for as long as you can. Try at least half a day but if it needs topping up as much as you say it probably wont need it. If the pressure holds on the boiler and then you open the valves and it drops you know the system had a leak on it.

. It's a simple job to pump up, there's a schreader valve on the vessel.

...and check the valvecore is in properly

You will have a small copper pipe outside pressure relief pipe. Check that this is dry when running and when turned off.

Another thing you can do is top up the boiler to the correct pressure. Turn it off and then turn the 2 isolation valves off at either side of the boiler. Do this for as long as you can. Try at least half a day but if it needs topping up as much as you say it probably wont need it. If the pressure holds on the boiler and then you open the valves and it drops you know the system had a leak on it.

thanks

Does it need topping up each time the system has been hot and cools down again?

If the bladder in the expansion vessel has failed then you would top the system up to operating pressure, the heating would come one and the system would weep out excess pressure through the safety valve. Then, when it cools down the pressure would drop.

Oh and that fernox leak sealer, I had a small leak under a freshly tiled floor and fixed things a treat!

just an update to this.

ideal engineer coming round again today, much to his disgust as "ive been an engineer for 20 years, i know what im talking about, ive told you, its not the boiler"
i cobbled up a little test yesterday, tied a plastic beaker underneath the pressure relief pipe on the outside of the wall.
this morning the system has lost pressure again and the beaker is nearly full. hopefully that will mean something to the engineer.

i asked my daughter again if theres any rhyme or reason to when it loses pressure, she says not. can be 3 times a day, 8 times a day, when the heatings on, when its off.....
overnight theres nothing on, no heating or call for water, and it loses pressure every night, its gone every morning.

Is the PRV in the boiler or elsewhere in the system? If it's opened due to excess pressure (expansion vessel empty etc) then it should be replaced.

Can I just ask, if the PRV has operated to release excess pressure then it MUST be replaced? Or is it just best practice?
Surely its just a spring loaded valve, so should be capable of operation a number of times? Or is it just because they rarely move and once operated have a habit of not sealing again properly?

Surely its just a spring loaded valve, so should be capable of operation a number of times? Or is it just because they rarely move and once operated have a habit of not sealing again properly?

This - it takes a tiny amount of debris to stop it from completely closing. I'm sure it's possible to clean them out - but I imagine it's a lot less hassle to simply swap them out if they are weeping.

I've no idea where the valve is, I'm no plumber 🙂

Sat here now waiting for engineer. Weirdly, the pressure has dropped again since daughter left this morning, but there doesn't seem any more water in the cup which has baffled me. Hopefully it'll mean somethings to the engineer.

I've topped the pressure up again so hoping it'll Starr dripping while he's here.

Still waiting, so been having a play. Switched heating on, pressure stayed at around 1.5 bar for 10 mins or so. Then it started climbing, up to around 3 bar, that's when the magic happened and the pressure relief valve must have kicked in and started dripping water into my cup.

Switched heating off, drips stopped, pressure dropped to 1.5 again. I assume if I'd left heating on pressure would have stayed 3 bar for longer, possibly being topped up by extra water? Dont know. Then when heating goes off it drops right down to zero.

Does that make sense to anyone? Boiler issue or system?

Thanks

Expansion vessel empty would be my guess - though someone did actually tell you how to check it early on in the thread.

Sounds very similar to the issue im having with my central heating system.
It was losing pressure whenever it was used. Turns out it was the expansion vessel had no pressure (no water out the schraeder valve fortunately), so once things warmed up the pressure increased and the PRV kicked in and dumped the water.
I increased the pressure to around 7psi which has improved things, but its still losing a little water from the PRV when then pressure gets too high. Having read up a little more, the expansion vessel needs pumping up to 10psi, which I still need to do.

I had the same when the flexible braided hose to the expansion vessel got blocked. Cleaning out the hose which was full of a hard black precipitate solved the problem.

Ours had two expansion vessels (#boastoftheday)
but the pipe linking them to the system was blocked, so all testing and re-pressurising of the expansion vessels did not work - took a while to locate that issue

Which reminds me - need to get a power flush or British gas wont come round to fix it again.

Expansion vessel empty would be my guess - though someone did actually tell you how to check it early on in the thread.

I had the same when the flexible braided hose to the expansion vessel got blocked.

he was a little scathing about my installer, even tho he'd originally insisted it couldnt be the boiler and must be 'the system'.
"the dirt wasnt in there when it left the factory" and also the 'filter/inhibitor' or whatever its called has been installed 'on the flow side rather than the return, so theres nothing to stop sh*t going through the boiler'.
that may or may not be true, i iz ignorant.

Well properly draining the water out of the system so there was no residual pressure left in there and then repressurising the expansion vessel to the correct pressure has sorted mine a treat. I drained probably 5-7 litres of water out of the system, so suspect I'd indvertantly overfilled the system over time.
No massive increases in pressure once the thing got up to temp and no pressure loss when fully cooled down overnight.
Plus the PRV seems to be holding too.
RESULT!
Hows the pressure on your system holding up sadexpunk?

Hows the pressure on your system holding up sadexpunk?

We're just checking that now.

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your engineers very generous.. your filter on the flow immediately invalidates two major manufacturers warranties.. whats the point of cleaning the water after its passed through the boiler..

already changed a pressure vessel and a prv this morning dont have to do the prv but it saves coming back if its goosed..and only 18 quid.

thanks for the comments chaps.

thought it was sorted, not so sure now. daughter says pressure was only just above the red when she left this morning. its better, cos it had gone completely before, but id have hoped it wouldnt drop at all :-/ she'll be reporting back tonight.
if it does, ill have to find out if any waters leaving the expansion pipe, as that will determine a boiler 'over-pressure' fault or a leak elsewhere wont it?

ill be having a word with the fitter tho, ask him why hes positioned the filter where he has. could there be crap getting stuck in the pipes constantly from now on then?

if your systems full of crap - in the rads and pipes.... and your putting in nice clean filtered water from the boiler...

guess where the craps going to end up before its captured by the filter.

im always amaized how much shit my magnaclean collects on an all new system with PEX pipes and delonghi rads filled with strong mix of fernox antifreeze(its an external boiler in teh country we get power cuts often) and inhibitor

b*ll*cks.

3 weeks after the engineer did whatever he did and fixed it, same thing has just started happening again.

what would this suggest to you experts out there? could it be the filter on the 'flow side'? i know a few of you think its in the wrong place but ive also spoken to 2 other gas safe engineers who've said thats not cut and dried, and that its 'boiler dependent'.

for whatever reason, the pressure is building until 3 bar, prv operates to dump water, pressure then drops to zero.
will have to ring Ideal again tomorrow......

What pressure is the system starting at?

Ideally 1 bar with everything cold, if the pressure is then reaching 3, either the expansion vessel is undersized (common on system boilers) or is knackered.

1 bar. and keeps being reset to 1 bar every time it dumps the water and drops to zero.

EDIT: if anything was undersized, then surely it shouldnt have been working for the last 3 weeks?

Good point about the vessel undersized, quite easy for an additional one to be added onto the pipe work.

How many radiators on the system ? Check the installation instructions of the boiler.

If the pressure gauge is is going from 1bar to 3bar with the heating on, that tells me it's the pressure vessel either undersized / needs re-charging / or faulty.

Is the filling loop 100% turned off ?? It could be slowly filling the system.

Possibly. Have you got lots of rads? Are more being used now if TRVs are opening?

its a 3 bed bungalow with a normal sized rad in each room. pretty sure the filling loops properly off.

seems strange that its been fine tho for 3 weeks, then just goes again.

pretty sure the filling loops properly off.

The valve taps might be turn fully off but that doesn't mean it isn't faulty slowly leaking into the boiler.

Filling loop should be disconnected when not in use to prevent the possibility of the water in your heating system getting back into drinking water supply.

What exactly did the engineer change / repair / tweak. If you can't tell us that all we're doing is guessing. Unless your engineer replaced the pressure vessel completely I would guess all he did was recharge it hence the fact it's now gone again. We had ours replaced before Christmas and it's been fine since, it did work for a while after I pumped it up despite the membrane having completely failed but it would have slowly lost the charge.

So disconnect the filler loop (legal requirement anyway) and work out exactly what was fixed last time around.

If you can't tell us that all we're doing is guessing.

We had ours replaced before Christmas and it's been fine since, it did work for a while after I pumped it up despite the membrane having completely failed but it would have slowly lost the charge.

So disconnect the filler loop (legal requirement anyway) and work out exactly what was fixed last time around.

thanks chaps, ill be on the phone to them this morning.....

Can you just get the system hot and turn off, then try releasing pressure from the expansion vessel. If it's dud then there will be very little air to release?

Not sure thats a good idea unless the OP wants to get scalded.
Better to check the pressure when COLD.

Sadexpunk where you?
I'll have a look if your near enough.

Not sure thats a good idea unless the OP wants to get scalded.
Better to check the pressure when COLD.

Sadexpunk where you?
I'll have a look if your near enough.

ive got a call booked for tuesday now.

Bigyinn... Should just be air but fair point. But when cold there would be less pressure in the expansion vessel anyway. Suppose you could achieve the same by just taking a reading from a bike pump.

ive been an engineer for 20 years

first off can we stop calling this guy an engineer. Unless he designs the boilers I very much he is an actual engineer.

OP first thing I would do is get the installer out (if you trust him) to drain the system and move the filter to the boiler inlet. Give it all a good flush and replace the PRV again and check the expansion vessel is adequate. I wonder if it would be possible to fit one where the splice in the boiler outlet piping will have to be when the filter is removed.

Do you have 1 radiator without a TRV where the thermostat is? If not you could be shutting off all the rads but the boiler still thinks it needs to be on, I would have thought it would detect the return flow was too hot before it did any harm though.

Did the installer supply the boiler or did you buy it and have him install? If the former then after so many faults I would think you soon have grounds to reject the boiler and ask for another brand to be fitted if the fault is due to the boiler and not some old part of your system. The filter in the wrong place does complicate things a lot but only as far as the manufacturer warranty is concerned, the installer on the other hand does seem to be responsible for putting it right.

just spoken to the installer andy, before i read your post. i asked about the filter placement and he said there was no room to put it on the return side near the boiler. the only other place would have been in the loft, and they tend to get forgotten about up there and not cleaned out yearly. not quite sure about that explanation myself, but for now ill accept it.
1. what are you suggesting goes in the 'splice'? another expansion vessel? should that really be needed?

2. all radiators have TRVs. the thermostat is on the wall in the hall. theres 1 radiator also in the hall with a TRV.

3. installer ordered the boiler from internet, delivered to our house and then installed it. obviously a legit sale tho as ideal have it on their records and are honouring the warranty.

thanks

The rad in the hall MUST NOT have a TRV on it.
The two will not get on and cause you issues as neither one knows which one is switching.

really?? ive had these thoughts to myself before..... whats best, crank the thermo up to max and control with TRVs individually, or set the thermo at reasonable temperature and then the TRVs and hope each one gets hot enough....

ive never heard that a hall radiator shouldnt have a TRV on it tho. and why just that one?
and why would they get confused? the wall mount will switch off as soon as it hits a certain temperature, and surely the rad will do the same, hit a temperature then switch off. in fact why would they [i]need[/i] to know what the other is doing?

oh, and i assume this is nothing to do with the boiler no? that shouldnt be happening regardless of whether the hall rad has a TRV....

thanks

1. Just a precaution if it did turn out you needed one. As you will already have a break in the plumbing there (if moving the filter to the correct location) then it could reduce the work. You shouldn't really need one though.

2. As hammy says above, you will get stuck in a feedback loop where they compete against each other. if the TRV is set lower then the thermostat will never shut off and the boiler keep going and going until it detects the return flow is too hot as the heat is not being dumped. Fully open the TRV or take the top off completely and put a cover cap over it so no one can adjust it.

3. My concern was just that he could try and walk away and claim no responsibility if you supplied the boiler. As he has supplied the boiler you may have more rights to have him make sure it all works correctly.

2. struggling to get my head around this one.... 😀

if every TRV is set low say, then you say the thermostat will never shut off as the 'set temp' on the wall is never reached and the boiler will keep going. firstly, why would the boiler keep going? nothing is calling for any further heat. and secondly, i have a TRV on the hall rad and the boiler isnt running all the time. so does that not disprove that theory? (not that im trying to disprove you :-))

EDIT: come to think of it its not on all the time as its on a timer too, 2 hrs morning, 2 hrs evening.

EDIT EDIT: so youre saying that for those 2 hrs on the timer, the boiler will be running all the time even if the rads have all reached their desired temp? whats happening to the hot water? just circulating around the system but bypassing the rads?
so the boiler is only ever doing what the wall stat is asking, doesnt listen to the rads at all.

thanks

with regards to the filter position - there is a reason you filter engine oil before it goes into your engine. Same principle here. Little bits of rust will come off the inside of your rads and find their way into the heat exchanger of the boiler where they may well get stuck before the filter on the outlet so by moving the filter to the return the water gets filtered just before it accesses the boiler. The inlet and outlet pipes are close to each other on the boiler so I don't see why it couldnt have been done properly first time round.

As for cleaning the filter it's part of the service. Put a sticker on the boiler saying the filter is in the loft and make sure he or whoever else does the service goes up there to flush it when doing the service.

the TRVs are mechanical with no electrical feedback to the boiler (unless you have a smart electronic system).

The boiler is controlled by the thermostat/programmer so is on when the timing says it needs to be on and only until it gets to temp. It will then fire up as and when needed to maintain that (I am simplifying so ignoring modulation etc)

If the TRV is set low then it shuts off the hall radiator so the hall doesnt reach the thermostat cut-off temp so, assuming your timer is still in an on period, the boiler will keep going. The other rads will then get more flow and eventually they will shut off. Then you have no rads dumping heat which the boiler doesnt like. It should self protect though before it needs to vent, or at least that is my limited understanding and how I would expect one to be designed. The PRV should be there in case of a more serious fault.

It would be worth a check though by removing the top off the hallway TRV and seeing how it goes. Also remove the fill loop if you can to rule that out. Might also be worth checking all the rads are hot to rule out air locks etc.

yeah good point. ill do that anyway, no matter what ideal bloke says. ill take a pic of the boiler when im there tuesday (just about to move into the house again after period of renting it out) so you can see the location.

thanks a lot

EDIT EDIT: so youre saying that for those 2 hrs on the timer, the boiler will be running all the time even if the rads have all reached their desired temp? whats happening to the hot water? just circulating around the system but bypassing the rads?
so the boiler is only ever doing what the wall stat is asking, doesnt listen to the rads at all.

You got it.

Only feedback is a mechanical one where the boiler can go "hang on, the water is coming back just as hot as it went out" Maybe on a system with a small expansion tank that is enough to trigger the PRV?

thanks, very interesting. not much of a plumber meself, is it easy to take the top of a TRV or do i need special 'plumber tools' 🙂

and is it the same result if i just crank the valve to max and leave it there?

It's a "hand job" if you'll pardon the expression.

No tools required 🙂

Just grab the ring and twist 😆
Thats the little one under the big knob...

I'm not knowledgeable at all when it comes to plumbing, so apols if this make no sense, but:

We had similar issues with a brand new pressurised system in our last house. Turned out that the previous ownners (or their plumber) had not added any corrosion inhibitor stuff to the water in the system. This caused corrosion in the pipes and the release of bubbles, which meant that the system was regularly over-pressuring when hot (air expands more than water when hot). The system then dumped excess pressure by releasing water though an overflow pipe and then dropped to a very low pressure once cold again. Queue me topping it up again, and again, and again.

I didn't believe the plumber to be honest, but adding the inhibitor fixed the problem. Problem was spotted because the water was always milky in appearance when bleeding the rads (full of little bubbles).

Hope you get it sorted - my system was driving round the bend when it was playing up.

ok, update time.

different engineer this time, and he thinks hes found the problem. hes thinking there was a pinprick hole in the expansion vessel, allowing water to get in slowly. he said there was water in the bit where it shouldnt be. id have thought the first engineer would have spotted that, but no matter, we're hopeful its sorted.
he also talked about the 'one rad with no TRV' but instead of the hall rad, he suggested the dining room, some distance away from the wall stat. something about if you do the hall rad then itll tell the wall stat that the house is hot enough too quickly, and the rest of the house may feel cold. seemed to make sense at the time and he took the valve off.

he also changed the vessel for a smaller one as he didnt have correct size. he looked at the system and how many rads i have (10 i think) and said that the 8 'something or other' should still be fine rather than the 10 that he removed.

he didnt make much of the incorrect placement of the filter, but said ideally it should be moved. i forgot to take a pic to post but he agreed space would be tight, and that if it was in the loft then theres access issues(?). he would suggest extra pipework in the tight spot to bring it out from the wall a bit. i asked if the extra 90 degree elbows would cause any 'flow issues' which he said was a fair point, maybe.
so im no better off with that really, but im still thinking it would be better off on the return side. dont think the original fitter will be too keen to move it at no extra cost tho and theres certainly no way i can force him to if its not a mistake as such. even some gas safe engineers are saying its no big issue :-/

thanks

Sounds like (or, I hope) you're sorted now. Only just seen your thread, but FWIW, we had the same problem for about 12 months, since we had the system drained for a bathroom refurb. Our local CH plumber (also a keen MTBer:)) serviced the boiler last week and fixed it - it was the pressure vessel. He said it's a fairly common problem and he see's a lot of people where other CH 'engineers' haven't spotted it - so people can end up throwing a lot of money at the problem. I'd got so worried about potential leaks that I'd been under some of the floors checking - the local fella fixed the problem with a new valve core (about 10p worth!) and a bike track pump.

HTH
p.s. If you need the number of our local guy, gimme a shout. He's in NE Sheffield but I guess he might cover Lincoln(?)

he also talked about the 'one rad with no TRV' but instead of the hall rad, he suggested the dining room, some distance away from the wall stat. something about if you do the hall rad then itll tell the wall stat that the house is hot enough too quickly, and the rest of the house may feel cold. seemed to make sense at the time and he took the valve off.

Put the TRV back on. The bloke doesn't understand how a thermostat works.

If you find that the hallway reaches temperature before the rest of the house, what you need to do is adjust the lockshield valve on the hall radiator to reduce the flow, and hence increase the time it takes to heat the room.

And this "engineer" is allowed to work with gas and unvented cylinders...

p.s. If you need the number of our local guy, gimme a shout. He's in NE Sheffield but I guess he might cover Lincoln(?)

Put the TRV back on. The bloke doesn't understand how a thermostat works.

If you find that the hallway reaches temperature before the rest of the house, what you need to do is adjust the lockshield valve on the hall radiator to reduce the flow, and hence increase the time it takes to heat the room.

And this "engineer" is allowed to work with gas and unvented cylinders...

whats his mistake then, cos it sounded reasonable when he explained it. 'a radiator remote from the wall stat needs to be able to 'waste excess heat' rather than the one near the wall stat doing so and knocking off the stat prematurely'.....

thanks a lot