Potted history - 18 months or so ago, our boiler was losing pressure and having to be topped up maybe weekly. Found a suspect radiator, which was replaced and all has been well since. Fast forward to 1st weekend in Dec last year when it was very cold, we were away and left heating off for a couple of days. Since then, boiler needing topping up almost daily so we clearly have a leak somewhere.
I cannot find the leak visually, all rads and valves seem fine and I cannot see any visual evidence of a leak anywhere (no damp patches etc). I've visually inspected every pipe I can access easily and can't see anything. Anyone got any tips for finding this or is it time to call in the experts?
is it a combi boiler or do you have a hot water tank?
Have you also checked around the boiler itself?
Combi - there is a towel under the boiler to check for drips but nothing. Also nothing coming from the boiler vent pipe (so not over pressured)
Heard a good one the other day. Perfume, strong and cheap the better. Place in system and kep a nose out.
Heard a good one the other day. Perfume, strong and cheap the better. Place in system and kep a nose out.
Sadly, with 3 boys in the house, everywhere stinks of lynx Africa so this might not work 😅
@5lab - how can I tell if it's the expansion vessel? Would that leak from under the boiler or just evaporate?
I’d suggest you have either a pin hole leak high up in the water cylinder and when you top up and the boiler boils the water, the hole expands and it leaks into the insulation jacket where it’s held and partially evaporated. Enough water then escapes from the system to expose the hole and you end up with air/water and stable pressure when cold. All the time you’re topping up, it’s reducing the effectiveness of the inhibitor, causing more corrosion and more wear.
The other option is a damaged PRV, but you’d be able to see this outside.
If you’re continually topping up, it’s unlikely to be the expansion vessel as it’d be almost full by now.
A final option may be a damaged automatic air vent on the top of the water cylinder, but again, this should be fairly obvious as soon as you open the top covers of the boiler.
Usually if the expansion vessel fails it's the air bladder that goes, which means you top it up until the tank is liquid full, then the next time the heating comes on the pressure rises rapidly and the PRV opens. So the symptom is pressure is either zero, or 3+ bar. Watch the gauge when the heating comes on and see if it moves.
Ours was the heat exchanger in the boiler when we had this scenario last year, boiler maybe 13 years old at this point. Not a cheap repair if it's that, probably 1/3rd the price of a new boiler.
You can tell if it's in the boiler or pipework by re-pressurising the system, closing the flow and return check valves to the radiators and monitoring the pressure for a few hours. If it maintains, the leak is in the radiator circuit. If it drops the boiler. This does unfortunately mean switching the radiators off for at least 12 hours which isn't ideal this coming week!
I'm pretty sure it's not the prv as I have a balloon over the end of the relief pipe and there's nothing in that. I'm assuming if it's probably losing about 2-300 ml or more to have a noticeable effect on the pressure.
Thats an interesting idea, i wonder if it works.
I wonder if you could train a dog to find a specific smell. Do plumbers like dogs?
I used to do Barrier membrane testing, which involved flooding a void with a tracer gas (helium in our case), and then wandering around with a geigercounter type tool that clicked when it hit a helium molecule.
It would involve drying out the system, and probably isolating the boiler, but im sure that would work.
Probably getting into the relms of calling a plumber though.
I bought a cheap caravan damp meter and went around all the walls where the central heating runs. Took a few readings but eventually found one leak on a joint in the concrete floor and another where the water pipe was rubbing on a gas pipe under a door threshold !! Right old PITA to dig out but each one a 10 min fix for the plumber after I'd done all the graft.
I'd left it for about a year before that but couldn't face another winter of constantly topping up. I also had changed the PRV and expansion tank.
Another vote for tissue paper around rad tails
Not sure why I didn't check this sooner, but I marked the pressure gauge after topping up about an hour ago and we're losing pressure even with no heating on (heating on twice a day, went off at 8am). Does that affect my checking?
I’d suggest you have either a pin hole leak high up in the water cylinder and when you top up and the boiler boils the water
Would the OP have a cylinder (it's a combi system)?
There's no hot water tank, but I assumed Daffy was talking about some part of the boiler. I could be wrong though!
If you top up the air in the pressure vessel and water comes out the valve then you know the diaphragm is shagged. As you know, don't leave the heating off in cold weather, the frost settings on the control or TRVs protect against frozen pipes (like unlagged pipes under the floor.
Thanks. Heating wasn't completely off, it was in frost mode. House temp did get down to about 8-9 degrees though. Frost protection kicks in at 5. The cold snap may have been a coincidence 🙂
I don't recommend it, but we found ours after we showed the babysitting grandparents how to top up the boiler and they left it in the open position by accident. A few days later water started coming through the ceiling and voila, we had found the leak.
Don't use tissues, use pale blue center feed roll as it changes colour nicely when wet.
If you can drain down the system and pressurise with air. It is alot less dense than water so you may well be able to hear it whistle as it escape.
Double check the pressure relief isn't dribbling out , it's sometimes returned through 270 degrees and aimed at the wall , or on a long drain leg.
Get a spaniel and train it to find smelly stuff and inject some aftershave or perfume into the system .
Been through this over xmas. <br /><br />
expansion vessel is pumped up by a normal car foot pump / track pump / hand pump.<br /><br />
there’s a car valve on top or side of it. Just like a car / bike. Let a tiny bit of air out. If there’s water coming out your vessels popped. If not then its not the vessel. <br /><br />
Depending in where the water goes if pressure vessel uou’d also have a puddle somewhere. On an old boiler, Ours drained onto the drive and there was a continual puddle. <br /><br />
this time filling the boiler 5x a day we ended up using trace and access off house insurance as finding anything under the floor is a royal PITA if its a tiny drip. Unless theres a load of rotten wood. <br /><br />
trace and access finds it, gets access to it then puts it all back together. They use thermal cameras and so on. Condition is you get your own plumber to sort it but we just paid the guy who the insurance used to find the leak to replace the damaged section. Cost £100 for the insurance part and plumber £40. <br /><br />
local plumber wanted over £1k per day as crawling around under floors is a sh1te job! And doing the tracing yourself you’ll be paying well north of £500 plus the repairs. <br /><br />
house insurance renewal price not impacted. As always we shopped around and got it for cheaper than last year with better cover for bikes too! Bonus 😁
couldnt fault the service. Access eith minimal damage and all put back together like you’d never know what happened. Laminate flooring coild be an issue getting proper colour match if you dont have spare boards from same batch. But the access people should be able to work round as best they can.
other option is to put some seal in one of the radiators, run the ch for a day then let it cool. It’ll fix small leaks but will fail again and if the leak is more than a dribble it wont work so best to find and sort if you’re topping up daily.
Ditto on trace and access here. We've had 2 leaks under the concrete floor slab now and cost a bloody fortune but went through house insurance. Our premium did go up though but I suspect that was because we claimed water damage and had a c.£5k payout to replace the hardwood floor, skirting and redecorate.
