• This topic has 31 replies, 14 voices, and was last updated 8 years ago by mcj78.
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  • Boilerpressuretrackworld… heating engineer advice required
  • mcj78
    Free Member

    Hi all,

    following on from the “have you had your heating on yet” thread – I most certainly have & it’s been causing a few problems that are driving me bonkers…

    The boiler’s been losing pressure, between 0.5-1.0 bar per day depending on how much the heating’s been on & I need to get to the bottom of it sooner rather than later in case I have an underfloor swimming pool gathering somewhere – only thing is, I can’t find a leak anywhere 😡

    Boiler is in the loft & all the pipes run straight down from there, behind a partition wall right down to ground level – there we have; a small hall with a door into the living room which opens into dining room, which in turn leads into the kitchen (an extension with nowt above it). We have a wee cellar under the dining room from which you can see right up the back of the partition wall up to the upstairs level where all the pipes run down from & there’s no sign of puddles in the cellar under the dining room, or apparently under the living room / hall floor as you can see the pipework running to the radiators there through a gap the height of the joists at the top of cellar & nothing looks damp – can’t see into the kitchen subfloor, so that’s a possible leak location…

    Upstairs there’s 3 bedrooms & bathroom all of which have radiators in – there’s no sign of leaks anywhere there & all the internal walls & ceilings are dry – with the amount of water we’ve been putting back into the system any leak upstairs would surely have made its way downstairs by now…(?)

    We have a friend who installs heating systems & he kindly fitted an external expansion tank he’d just removed from another install which was being upgraded as the original was apparently on its way out, I then replaced the schrader valve on the new one as a matter of course & recharged the system to the right pressure & crossed my fingers. Did it work? Did it balls.

    So, I then had a heating engineer out to have a look at the boiler itself – the overflow was apparently dry so he ruled out a faulty pressure relief valve & suggested I run a can of Fernox F4 Express through it to see if that helped – then we’d at least know if it was a leak, that didn’t work either…

    Chatting to the neighbours they mentioned they’d seen a fair bit of steam coming from the flue & were wondering if that might have anything to do with it – the boiler’s about 10-15 year old condensing number & our boiler engineer guy said the steam wasn’t likely to be anything untoward & that condensing boilers usually generate more steam from the flue…

    Anyone any ideas? I’m going slowly mental here, although I am getting good exercise running up the loft ladder every day – every cloud & all that…
    J

    wrecker
    Free Member

    We have a friend who installs heating systems & he kindly fitted an external expansion tank he’d just removed from another install which was being upgraded as the original was apparently on its way out, I then replaced the schrader valve on the new one as a matter of course & recharged the system to the right pressure & crossed my fingers. Did it work? Did it balls.

    Keep checking the pressure in the tank? The bladders in these can go (if bladder type)

    andyl
    Free Member

    You will get steam out of a condensing boiler as the flue temp is lowered by the heat extraction so it more likely to condense sooner on exiting into the atmosphere.

    I don’t know if an internal corrosion fault could cause central heating water to get into the burner and (through the heat exchanger?) and add to that. I guess it is feasible with my basic understanding of boilers.

    What boiler is it and what type? (system, combi etc)

    Check all your rads for weeping valves/joints by wrappng toilet paper round anywhere that could leak.

    I guess the other thing could be the pressure vessel inside the boiler if fitted but don’t know much about that kind of fault.

    Currently have guys in and our boiler in pieces as EDF contacted us to say we’ve been using 2x our normal winter gas over summer (£1000 of gas this year so far). Landlord is looking worried it’s something wrong with the system, which is ancient, but so far all they have found is a worn jet and a loose pipe on the burner but not had any gas smells. Best case would be a faulty meter but they normally under read.

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    mcj78
    Free Member

    Hi Wrecker – yeah i’ve been checking the pressure on the “new” expansion tank (cold) & it’s been constant, set it to approx .8 bar & set the boiler to roughly 1.5 bar to make sure there’s enough pressure from the system to make the expansion vessel work. The old’s still in situ inside the boiler but has been completely bled of air to make sure it’s not still trying to move & affecting pressure slightly.

    J

    mcj78
    Free Member

    Andy – it’s a Worcester Bosch CC1 gas fired condensing combi, I had read somewhere that a corroded heat exchanger could allow water in which is then instantly boiled off & escapes the flue as steam but the engineer i’ve had out didn’t think it was that…

    J

    Flaperon
    Full Member

    I don’t know if an internal corrosion fault could cause central heating water to get into the burner and (through the heat exchanger?) and add to that. I guess it is feasible with my basic understanding of boilers.

    If the heat exchanger leaks enough to drop one bar overnight you’d have an obvious leak running down the condensate drain with the boiler off. (Unless you mean 0.1 bar/day?).

    Mine dropped by about this amount and I tightened every valve and fitting in the house, checked everything, swapped air vents, you name it I tried it.

    In the end I squirted a can of Fernox leak sealant in through the filling loop and that solved the problem instantly. Pressure’s not budged in over a year.

    mcj78
    Free Member

    Flaperon – yep, unfortunately it’s losing 0.5-1.0 bar per day, was hoping the leak sealer would have done something as then there would have been something to aim for but now it’s just frustrating… I cleaned the condensate trap out & it was full of crap from recent water works in the area, might be one to keep an eye on though – i’ll maybe disconnect the condensate pipe & run it into a bucket to see how much is coming from it

    j

    trail_rat
    Free Member

    First thing id do is tie a baggie over the prv outlet.

    Ianap.

    mcj78
    Free Member

    Trail Rat – the engineer I had out had the pipe off the prv & said it was bone dry, I thought once the prv opens the seal’s gone & it has to be replaced?

    When in the shower (or running a bath) the water runs hot & cold too – if that helps any?

    J

    mcj78
    Free Member

    Cheeky bump for the tea-time massive before I take a big hammer to it, any other ideas? 8)

    alexb17
    Free Member

    I’ve had a similar problem with my boiler over the past few months. Try draining a radiator into a bowl and check to see if there is debris in the water. Our problem was that the system wasn’t flushed after instal and dirt was blocking the connection to the expansion vessel. The system would heat up, expand, dump through the safety release valve, cool overnight and then not have enough residual pressure in the morning to allow the burner to fire. Had the plumbers flush it through a couple of times and add inhibitor and have had no problems since (touch wood).

    divenwob
    Free Member

    Combi running hot and cold sounds more like diverter valve.
    Could be an internal leak letting the heating water out via the taps, ie heat exchanger.
    As trail rat says,try a bag over the prv just to make sure.

    mcj78
    Free Member

    Cheers guys, when the water goes cold the radiators do start to warm up so the diverter valve had been something I had thought about but wasn’t sure how that would cause the pressure to drop, is that a possibility then? When I cleared out the condensate trap a couple of weeks ago when the boiler wouldn’t fire, it was jam packet with crap from recent water works in the area – had been losing pressure before that & thought that was related somehow but apparently not, it’s bursting my tits & I don’t want to rip the whole thing out in case it’s a stupid £30 part… Or even a stupid £200 part for that matter, but dunno if I fancy throwing more than that at a 15 year old boiler 😕
    J

    Mole
    Free Member

    You definitely sure the blow off pipe eternally is bone dry?

    Greybeard
    Free Member

    Speculating, based on the shower going hot and cold, I but don’t know the layout of the boiler (IANAHE). Combi boilers work on HW priority, ie, if the CH is on and HW is requested, the diverter valve put the water into the heat exchanger. So if it’s switching back to to CH while you’re using HW, the boiler “thinks” the HW is adequately hot (so it goes back to CH). If there was a leak in the heat exchanger, from the primary circuit into the HW, but just local to the sensor, that might do it?

    If you turn off the HW, does the boiler still lose pressure?

    mcj78
    Free Member

    The blow off pipe feeds into an internal soil pipe that runs through the middle of the building so not easily accessible, not ideal, when the engineer came out he took the pipe off the valve & checked inside it for any sign of water but it was apparently bone dry (his words)

    The pressure drop wasn’t immediately noticeable but became more apparent when we fired the heating on, so it was losing pressure slower when we were just using the hot water, we only moved in a few months ago & I bled all the radiators at the time & thought the pressure drop was just some residual air moving round the system & venting off when it reached the boiler… NOPE 😐

    Been down the dungeon again & I think there’s isolation valves on the pipes heading to / from the kitchen radiator so to rule out a leak there I’ll turn those off when I get a chance over the weekend & see if that makes any difference

    Cheers for the replies all – I’ll get to the bottom of this if it’s the end of me!
    J

    fluxhutchinson
    Free Member

    You do remove the pressure from the system when setting the expansion vessel pressure dont you?

    When the heating is on does the pressure rise a lot? Did the engineer check the prv when the heating was on?

    Try isolating the boiler on the central heating isolation valves. for 24hrs if you can. If the pressure drops you know its more than like something with the boiler. If it holds and you open the iso valves and then it drops its more than likely on the system some where.

    bigad40
    Free Member

    I will have a look for you if you’re near me.
    You have a leak. Could be heat exchanger/s could be somewhere else.
    Leak sealer will not work!

    mcj78
    Free Member

    Flux – yep, drained the boiler then released the air from the vessel, changed the schraeder valve over, set it to just under 1.0 bar then re-pressurized the boiler via the filling loop to about 1.5 bar, when the heating’s on the pressure doesn’t seem to rise at all, just drops slowly… I could give the isolation taps a try – just need to work out which valves to turn, the gas inlet one is the yellow one right? so other than that there’ll be the mains water inlet & the heating out / return pipes? Anything else i’m missing?

    Bigad – very kind, i’m in Renfrewshire, going to contact the heating engineer again & see if he has any other ideas but in the meantime…

    I shall first try to isolate the heating and use the hw as normal to try & determine if it’s a boiler or pipework leak, then if it seems like a pipework issue i’ll isolate the kitchen radiator via the valves in the dungeon & see if that makes any difference…

    Cheers guys – next i’ll try to charge the missus £60 per hour (to be redeemed as bike parts allowance) for the time spent on this shitting thing! 😆

    John

    Smudger666
    Full Member

    my 2p worth…..

    its good practice to fill the system to the cold fill pressure of the expansion vessel (or actually, the other way around – pressurise the vessel tot he cold fill pressure of the system.

    There is a direct relationship between the cold fill pressure/safety valve pressure setting/system volume/system design temp rise.

    it is good practice to put the discharge pipe through a tundish if the exit point from the pipework is not easily visible(as in this case) – this give a visual indication of discharge.

    have you checked that the ‘new’ EV is holding its charge? i.e pressurized it to 1bar cold and then checked 12/24 hours later? an expansion vessel either works, or it doesn’t – what symptoms indicated that ‘it was on its way out’?

    your last post – when the heating is on the pressure doesn’t rise – indicates a leak and I’ll bet it is the safety valve. the pressure HAS to rise unless there is a leak.

    mcj78
    Free Member

    Smudger – some good points there, I checked the new EV the day after fitting it & the cold pressure was the same so it appears to be fine – when the heating’s on it warms up on one side so there’s hot water getting into it. Our friend who fitted it had a similar problem with his boiler & the EV was the culprit so we put the new one on the system to see if it cured the problem as it would have been an easy fix as he had a new-ish EV in his van.

    When the engineer came out after that he checked the old one & it was full of water with no air pressure in the air side so he thought that the bladder in that might have been leaking but it apaprently wasn’t the root cause of the pressure problem. Is there any easy way of me checking the safety valve without getting the engineer back out – could I disconnect the pipe & stick a bucket under it?

    Cheers again!
    J

    Smudger666
    Full Member

    yes you could do that – its difficult to estimate how much water your pressure drop will equate to but a bucket should be ok – keep an eye on it.

    its likely that thats the problem (safety valve) – if the internal EV was actually leaking rather than just the bladder burst, it would be immediately obvious as there would be water coming out of the boiler.

    these boiler safety valves will often have rubber/plastic seals that are designed for one off discharges in the event of a system issue that then gets fixed and the valve reseats.

    if they are continually used for daily discharges, the seal can be damaged by the pressurised water cutting a channel in the seal as soon as the valve starts to lift – I’ve seen this on many DHW safety valves where the system is designed to discharge to waste. a small leak of pressurised water will soon cut through rubber/plastic.

    even if you catch the issue quick, a CH system is/can be full of all kinds of gunk and it only takes a small piece of debris to allow a leak.

    hammyuk
    Free Member

    As Smudger said – had this very issue.
    It lead to a blown pump seal that was allowing water past the shaft and out of the PRV.
    Nothing obvious until we did the talc trick.
    Would lose around 0.5 overnight and not fire the HW.
    £85 for the pump which came with a new PRV (£30 on its own)

    mcj78
    Free Member

    Hammy – i’m guessing the talc trick is just to fire some into the PRV exit pipe & see if it’s there the next day?

    J

    hammyuk
    Free Member

    Kinda – or below it anywhere where water might lay

    mcj78
    Free Member

    Hi again all – bit of “progress” to report… 😕

    Over the weekend the heating didn’t seem very warm, even with the thermostat set to 20+ degrees & the hot/cold water issue was becoming more & more frequent so I isolated the heating circuit via the 4mm allen bolt valves on the out/return pipes & topped the pressure in the boiler up before I went to work yesterday morning – got back 12hrs later & it had gone from 2.0 to 1.0 bar so looks like the pressure is dropping from the boiler side of things after all…

    I then opened the valves again & turned the heating on to check the flow but when requesting the heating it wouldn’t fire – hot water was fine as I checked that too, but when I tried to top the pressure up again it wouldn’t have any of it – the water was apparently going straight into the heating circuit as I could hear water flowing through it. I checked the pressure of the external EV & it was up about 2.5 bar so I decided to switch it off as the pressure on the boiler was lower again now & I didn’t want to run the risk of it running completely unpressurised if someone turned on a hot tap. I didn’t dismantle the PRV pipe connection at the time but it did feel pretty warm so water might well be exiting via there – have contacted the boiler guy again & just waiting for him to phone me back at present, does it sound like the diverter valve now? Would that cause the boiler to dump pressure like that?

    Cheers
    J

    santacruz
    Free Member

    It sounds like you are local to me ‘bigad40’ I have an interesting CH challenge. What is your email addy or you can contact me via my profile.

    mcj78
    Free Member

    More “progress” on mine – I checked the CH isolation valves again as I was stumped as to why I couldn’t get pressure back into the boiler & yep, you guessed it – I am a fanjo & one wasn’t fully open so back to square one again… 😳

    I then checked the condensate drain for excess run off so I disconnected the plastic drain pipe underneath the boiler & fed it into a bucket – heating back on & an hour later there was over a litre of water in there – sounds like slightly more than condensate is running into it & so it appears the heat exchanger is shot, don’t know if this would cause the hot water to run hot & cold though? If it’s a heat exchanger + diverter valve I think it’ll be new boiler time…
    J

    Flaperon
    Full Member

    http://www.screwfix.com/p/monument-tools-flourescein-drain-dye/31595

    Stick this in (might need to depressurise the system and drop it into the top of a towel rail or similar); you’ll know straight away whether it’s escaping through the heat exchanger.

    mcj78
    Free Member

    If it’s leaking from the HE will the dye end up in the condensate pipe then I take it?

    Cheers!
    J

    Flaperon
    Full Member

    That’s the idea. 🙂

    mcj78
    Free Member

    I’m getting good at this now 😉

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