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Author: Subject: central hearting problem
smart51

posted on 14/10/20 at 08:05 AM Reply With Quote
central hearting problem

My central heating is losing pressure. I disconnected the pipe to the pressure relief valve yesterday and put a bowl under it. There's not a drop of water in there, so it's not a leaky PRV. There's no sign of water or damp in any of the ceilings or walls. How can I find out where the water is leaking?
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HowardB

posted on 14/10/20 at 09:16 AM Reply With Quote
it could be an air leak,. have you bled the system?
how old is the system?





Howard

Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)

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smart51

posted on 14/10/20 at 11:36 AM Reply With Quote
No air comes out when bleeding the radiators if the system pressure hasn't dropped to zero before refilling. The entire system is 4 years old.
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Davedew

posted on 14/10/20 at 12:15 PM Reply With Quote
Ours was losing pressure without any signs of water.
Turned out to be a slight weep around the pin under the TRV was causing it.
Take the TRV's off of the radiators and see if there is any signs of water.

Replaced the radiator valve and ours has been fine ever since.






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smart51

posted on 14/10/20 at 01:19 PM Reply With Quote
The valves under the TRVs are all dry. No signs of previous leakage.

Would turning off all the TRVs isolate the radiators? I'm wondering if I can narrow down the leak to pipes or rads.

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Davedew

posted on 14/10/20 at 01:37 PM Reply With Quote
You would have to close the TRV's and lockshields at the other end of the radiator to totally isolate them from the system.
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Russell

posted on 14/10/20 at 02:33 PM Reply With Quote
Could be a leak in the expansion vessel?
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smart51

posted on 14/10/20 at 02:39 PM Reply With Quote
quote:
Originally posted by Russell
Could be a leak in the expansion vessel?


A leak of water into the air side of the expansion vessel? I guess that would explain why no water has been seen on the outside.

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Russell

posted on 14/10/20 at 03:26 PM Reply With Quote
quote:
Originally posted by smart51
quote:
Originally posted by Russell
Could be a leak in the expansion vessel?


A leak of water into the air side of the expansion vessel? I guess that would explain why no water has been seen on the outside.


Yeah, that's what I meant. Eventually you might get leakage from the vent/condensate pipe to the outside or from the boiler itself. I've experienced this mysterious persistent pressure loss with a couple of systems on different premises and both times the diaphragms in the pressure vessels had pinhole leaks. It's something else to consider... Both were Worcester Bosch combi boilers by the way.





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smart51

posted on 14/10/20 at 05:09 PM Reply With Quote
quote:
Originally posted by Russell
quote:
Originally posted by smart51
quote:
Originally posted by Russell
Could be a leak in the expansion vessel?


A leak of water into the air side of the expansion vessel? I guess that would explain why no water has been seen on the outside.


Yeah, that's what I meant. Eventually you might get leakage from the vent/condensate pipe to the outside or from the boiler itself. I've experienced this mysterious persistent pressure loss with a couple of systems on different premises and both times the diaphragms in the pressure vessels had pinhole leaks. It's something else to consider... Both were Worcester Bosch combi boilers by the way.


Yep, mine is a Worcester Bosch Greenstar 29CDi.

I've had all the radiators closed at both ends (except the towel rails) for a couple of hours. The pressure hasn't dropped. I've had the system running and not running. I'll leave it a bit longer, then turn 1 rad on at a time and see if the pressure loss comes back.

[Edited on 14-10-2020 by smart51]

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cliftyhanger

posted on 14/10/20 at 07:48 PM Reply With Quote
What sort of timescale/pressure loss are we talking? 1bar in 24 hours?

Had a issue with a new system the plumber gave up trying to find. Furious, I found the leak under the ground floor, obvious really as no signs of damp ceilings/carpets anywhere. Plumber had not pushed a speedfit fitting on far enough...idiot.

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smart51

posted on 14/10/20 at 08:04 PM Reply With Quote
quote:
Originally posted by cliftyhanger
What sort of timescale/pressure loss are we talking? 1bar in 24 hours?

Had a issue with a new system the plumber gave up trying to find. Furious, I found the leak under the ground floor, obvious really as no signs of damp ceilings/carpets anywhere. Plumber had not pushed a speedfit fitting on far enough...idiot.


over the weekend it was losing 1 bar in 24 hours. Yesterday it was 1 bar in 8 hours. Earlier today it was 1 bar in 2 hours. Since I switched the radiators off mid afternoon, it seems to be stable.

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cliftyhanger

posted on 14/10/20 at 09:02 PM Reply With Quote
So fast enough it should be obvious.
Good luck with the investigations, it can be infuriating but hopefully soon sorted.

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coyoteboy

posted on 15/10/20 at 12:16 PM Reply With Quote
I found endless loss of pressure in my WB boiler came from rads - not the TRV, but the upper plug opposite the bleed valves - they were oozing ever so slightly (o-ring dead) and because the rad is hot, it just evaporated off without leaving trace.

I also found that I had a minor leak at a lockshield where the installer has used microbore into an 8mm to 15mm converter for the valve, then not really tightened up the compression joint fully - again, tiny drip that evaporates off quickly.

I'd considered adding UV tracer to the system as I would with car systems, but then I swapped all the rads after a screwfix sale (10 a rad!) and now have a fully re-plumbed house so not much point.





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nick205

posted on 15/10/20 at 02:01 PM Reply With Quote
Interesting thread.

We have a 15 year old Worcester Bosch Greenstar 30Si combi boiler. over the past couple of years the central heating pressure slowly dropped. Checked around the house several times and no obvious signs of water leaks from the central heating pipes or rads. We then had an old radiator replaced with a new one when it needed moving. Turned out to be a weeping joint at the entry point, when the heatng was on it evaporated the weeping leak before it left any sign of leaking water. Without having that radiator dismantled I doubt we'd have found the leak.

Since then the boiler's held pressure without an issue.

Might be worth wrapping some kitchen roll (or even blue workshop roll if you have any) around the radiator inlet/oulet points to see if it shows anything.

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HowardB

posted on 15/10/20 at 02:31 PM Reply With Quote
I have experience of the leaking pressure vessel and also the pressure loss on rads and joints,. it is a real pain.

Sequential isolation is a good next step.





Howard

Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)

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mark chandler

posted on 15/10/20 at 04:04 PM Reply With Quote
My boiler was dumping water through the overpressure valve in the boiler, turns out these are quite a common failure and as hot water gets pushed out it disappears very quickly out the external vent.

Mine got worse after topping up I testing the big red button to drop a little pressure - that finished it off.

15 posted for a new one, 6 months later not dropped at all.

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cliftyhanger

posted on 15/10/20 at 05:22 PM Reply With Quote
quote:
Originally posted by mark chandler
My boiler was dumping water through the overpressure valve in the boiler, turns out these are quite a common failure and as hot water gets pushed out it disappears very quickly out the external vent.

Mine got worse after topping up I testing the big red button to drop a little pressure - that finished it off.

15 posted for a new one, 6 months later not dropped at all.


It seems that on a used system, the PRV's are a use once and never seal again component. I guess crap in the water, though tiny, stops them seating properly.
Trouble is, on some worcester boilers, it is a 200+ as the boiler needs stripping to get to teh valve,helpfully positioned at the back behind just about everything. And on older ones, yes, 10 minutes and 15. (that took me longer to find the final 2 case screws than changing the valve)

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smart51

posted on 17/10/20 at 12:00 PM Reply With Quote
The plumber has just been. Says the expansion vessel is good. He turned off the isolation valves on the central heating part of the boiler and said toleave it a few days. If the pressure drops, the leak is in the boiler. If it doesn't the leak is in the pipes. Fair enough.

An odd observation from the last few days. From 7:30 in the morning, when I fill it up, to maybe 7:00 in the evening, it loses no pressure at all. From 7pm to 10:30, it might lose half a bar. If I fill it up at 10:30 by the time I check it again at say 2am, the pressure has dropped to zero. If I fill it up again, it has dropped to zero again by 7:30. Why would it only leak at night?

[Edited on 17-10-2020 by smart51]

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ttalps2000

posted on 18/10/20 at 07:48 PM Reply With Quote
its colder in the house, metal shrinks when it gets colder, a small gap opens and water leaks out? Warms up in the day the gap closes again? ASlmost sounds like a dry solder joint somewhere!
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