CH boiler losing pressure

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  • CH boiler losing pressure
  • Premier Icon thisisnotaspoon
    Subscriber

    It drops from 1 bar to ~0.2 over the course of a month, or as often as I remember to check it, if it’s left long enough eventually the heating doesn’t come on but I remember to check it when the the towel rail starts glugging because it needs bleeding (more on that later). So it’s losing ~5l a month to somewhere.

    It’s been doing this the whole time we’ve lived here. It’s not the PRV or expansion tank, I’ve checked. And there’s no damp patches (parquet floor downstairs so it should be obvious if there was a leak).

    I was convinced it was the main boiler burner part that was leaking because there would occasional be a puddle under the boiler (plumber couldn’t find the fault, but I’ve concluded he’s not that great) and it eventually died due to the whole thing becoming flooded with water right back to the gas valve, plumber diagnosed a blocked kitchen outlet and no air gap/tundish for the condensate drain so the boiler was the first thing to back up (it’s under the stairs at floor level). Nothing else ever appeared blocked so I’m not convinced, but I guess a partial blockage wouldn’t be obvious if the water was just sat in the pipes below the level of the sink, washing machine etc.

    A few months before that we had a new bathroom and en-suite put in. And the towel rails are always the thing that needs bleeding when the pressure drops. Rarely the actual radiators. Could be coincidence that the towel rails just happen to be the first thing in the system after wherever the leak is?

    So either:
    1) There’s a leak somewhere, probably in the pipes under the concrete slab downstairs and not worth dealing with, just keep topping up unless it suddenly gets really bad.
    2) It was the boiler leaking, and now by coincidence it’s the the new towel rails, but we never notice as the towels absorb it.

    Should I worry or waste any more effort trying to find the leak, or should I add some stop-leak to the system (reluctant given that it’s a new boiler with a warranty), or just keep topping it up and bleeding the towel rails?

    Ohh and the 3-port valve has a mind of it’s own, we get HW and CH at the right times, but tend to also get CH when the water comes on? This isn’t the worst feature in the world as it means the towel rails warm up for an hour even in summer (the rest of the rads are on TRV’s).

    Premier Icon jam bo
    Subscriber

    but tend to also get CH when the water comes on?

    most combi boilers dump excess heat into the CH system when running HW.

    slow leak on a compression fitting could easily be evaporating on hot pipes. can you get UV dye to put into the system to find leaks??

    And there’s no damp patches (parquet floor downstairs so it should be obvious if there was a leak).

    Might not be as obvious as you think. I assume that all your pipework is surface mounted and not concealed anywhere?

    so it’s losing ~5l a month to somewhere.

    5000ml over 30 days equates to  under 7 ml per hour in a warm house. It could be evaporating as quick as it’s leaking and you’d never see it.

    jimw
    Member

    We had a year old Worcester Bosch boiler start to loose pressure. Spoke to them on the phone, they suggested checking for leaks as ‘couldn’t be the boiler’. No leaks anywhere, got to the point that it would lose 1bar overnight and I was topping up pressure every morning. Still no sign of water. They came out ‘ we’ll have to charge you if there is no fault’ Engineer turnes up, ‘Absolutely positve can’t be the boiler’…and it was a porous heat exchanger dumping the water down the condensate pipe which joins another so was difficult to see. I did get an apology.

    Premier Icon rogermoore
    Subscriber

    Had something similar once in a flat we were renting – plumber couldn’t find anything. In the end they put some kind of sealant into the system which would plug any tiny holes it found and this sorted it.
    RM.

    At a guess, the towel rail is the highest point in the system, so that’s where the air goes? But yes, if that section of pipework is new, that would be where I would start looking. Check the connections under the towel rails.

    A bit of a determined leak hunt might yield benefits, although there will be plenty you can’t get at.

    Check that the 3 port valve motor is doing the business. If the rads are getting properly hot with HW only, then chances are you need a new one or the whole valve is stuck open.

    How can you be certain that it’s not the PRV venting a drip now and then?

    We’ve just had a similar issue, bit easier to detect and fix though (leaking auto air vent). That was probably dumping 1 bar every few weeks, and there was a visible drip from the boiler casing. If your vent is in a position where it drips onto something hot, then as others have said, it may be evaporating straight off.

    Premier Icon thisisnotaspoon
    Subscriber

    Might not be as obvious as you think. I assume that all your pipework is surface mounted and not concealed anywhere?

    All the downstairs is set under the concrete, upstairs is under the floorboards. So there’s actually very little that’s visible.

    How can you be certain that it’s not the PRV venting a drip now and then?

    Plastic bag over the outlet for a month.

    Check that the 3 port valve motor is doing the business. If the rads are getting properly hot with HW only, then chances are you need a new one or the whole valve is stuck open.

    The motor works, and the valve isnt stuck, I did wonder if it was wired back to front or something.

    upstairs is under the floorboards

    I’d be lifting the floorboards underneath your new towel rail.

    My money is on the fitter having racked  a joint under the floor  whilst fitting the new towel rail.

    I have the same thing in my house underneath a tiled bathfoom floor but just live with it as it’s on the ground floor and the minimal leak is straight into the solum.

    Premier Icon senor j
    Subscriber

    I had one recently – tiny leak on the secondary heat exchanger seal.
    Bit of tissue inside the boiler proved it.

    retro83
    Member

    Put tissue paper or coloured chalk under/round all the visible pipe fasteners. Mine all felt tight and dry but I still had a very minor leak on one. You would of course never notice as it on a hot pipe it evaporates quickly but it marks the chalk.

    The rads getting hot when you run the tap is also ringing alarm bells as I had that symptom on my boiler shortly before the (forgotten the name) valve failed completely and flooded my loft.

    My money is on the fitter having racked a joint under the floor whilst fitting the new towel rail.

    That was my first thought. Bet his is tiled too, though.

    The motor works, and the valve isnt stuck, I did wonder if it was wired back to front or something.

    So it still happens when you manually close the valve?

    servo
    Member

    The reading on my boiler pressure meter was always low but it would recover very quickly when topped up. Turned out the expansion vessel needed to be topped with more air pressure. Plumber used my bike pump!

    Premier Icon Mary Hinge
    Subscriber

    Towel rail getting hot when you run HW is NOT necessarily a cause for concern.

    Depending on how it’s set up the electronic valve doofer automatically directs some heat to the towel rails so you have warmed towels when you get out of the shower.

    A previous old combi of ours used to loose pressure over a couple of weeks. Turned out to be the expansion vessel was leaking. How have you confirmed that yours is fine?

    Premier Icon thisisnotaspoon
    Subscriber

    The rads getting hot when you run the tap is also ringing alarm bells as I had that symptom on my boiler shortly before the (forgotten the name) valve failed completely and flooded my loft.

    Not that sort of boiler, the boiler just heats a closed loop which the 3 port valve then sends to the coil in the HW tank, the CH or both. The 3 port valve is controlled by the timer.

    A previous old combi of ours used to loose pressure over a couple of weeks. Turned out to be the expansion vessel was leaking. How have you confirmed that yours is fine?

    Usual symptom of the bladder leaking would be the pressure shooting up and the PRV opening when the boiler comes on.

    Depending on how it’s set up the electronic valve doofer automatically directs some heat to the towel rails so you have warmed towels when you get out of the shower.

    I did wonder if it was something like that, but it’s not that complicated a system, there’s only two destinations for the closed loop, it’s either sent to the HW tank coil or to the CH rads. And it’s the hall rad that gets warm (the only one with the TRV set to max as it’s in the room with the thermostat).

    I agree, a clever way to do it would have been to put the towel rails on the return part of the HW loop.

    Usual symptom of the bladder leaking would be the pressure shooting up and the PRV opening when the boiler comes on.

    And easily confirmed when water comes out of the schrader valve on top when you go to recharge it.

    Premier Icon Scapegoat
    Subscriber

    Yep, check under floorboards and any other voids. My downstairs boiler started to lose pressure and a search eventually discovered that mice had nibbled the polymer elbows/compression fittings under the floorboards.

    I have just this week had the exact symptoms you have with my 3yr old boulder. It was doing my head in. No leaks ANYWHERE, my pal who fits kitchens checked all the radiators and boiler for leaks but couldn’t find anything. I was topping up every 2 days.

    Purchased the boiler through a very helpful chap on here from the Northeast. ideal model and 7yr warranty. Called them up and they arranged to send someone on Wednesday. We actually hadn’t got around to the yearly service so organised that for Sunday. Plumber came around, serviced it and said in seconds it was our heat exchanger leaking. It was bloody dripping into some take off pipe so there was zero evidence from outside the boulder.

    Wednesday came, ideal plumber fitted £300 worth of parts over about 3hrs and it’s all hunky dory again. Really really pleased with the service and help with the warranty.

    Not sure if this helps but it was a mystery why we were losing so much pressure so quickly with zero evidence of a leak. The plumber said it was amazing the leak found itself to this take off pipe.

    I have just this week had the exact symptoms you have with my 3yr old boulder.

    You are Fred Flintstone and I claim my five shells.

    Premier Icon spennyy
    Subscriber

    Have you looked at the prv? If the fitter bled excess water out if the system via it instead of from the radiator bleed valves then it’s probably knackered the valve and needs replacing. Top up and bleed the system, fire it up and go stand outside and look for water being blown out.

    sharkbait
    Member

    Is the pipework in the concrete copper of plastic?

    If copper then the bad news is that concrete will corrode copper and cause leaks.

    Premier Icon Smudger666
    Subscriber

    If copper then the bad news is that concrete will corrode copper and cause leaks.

    source?

    Premier Icon thisisnotaspoon
    Subscriber

    source?

    IIRC only if it’s wet and reinforced concrete. If it’s saturated then you get galvanic corrosion owing to the salts in the concrete.

    More likely the expansion and contraction of the copper would cracked it.

    stevextc
    Member

    Is the pipework in the concrete copper of plastic?

    If copper then the bad news is that concrete will corrode copper and cause leaks.

    Or if its old enough a non soluble flux might have been used…. nasty if its under concrete

    sharkbait
    Member

    source?

    I should have said ‘can’ rather than ‘will corrode’, but Google it. Theoretically it shouldn’t happen but it can in some circumstances. Sometimes it’s the soldered joints that suffer

    Nowadays you’ll probably find plumbers will run copper through a plastic pipe before it goes through concrete.

    Assuming there are no leaks. My monies on the expansion vessel bladder having a slow flat.

    You can pump the bladder up (this is done in a service) with a bike pump. You can measure the pressure once you have relieved the system pressure via the blow off valve using a tyre gauge, they are typically charged to 1 bar.

    You can just keep pumping them up every so often and topping up the CH system but a proper fix is a new vessel.

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