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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Daily boiler pressure loss - Help! https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1292519262 Message started by tomoose on Dec 16^th, 2010, 5:07pm

Title: Daily boiler pressure loss - Help!
Post by tomoose on Dec 16^th, 2010, 5:07pm

Hi,
I'm new to this forum, but am at my wits end with my central heating system at the minute, and hoping some of you guys can help. I'll expain the situation briefly:

Gloworm 30cxi condensing combi boiler, installed in July 2007. I live in a 3 story mid terrace (basically, two floors plus a basement which includes the kitchen and cellar). The boiler is installed in the kitchen, but there is no central heating down there, so no pipework under concrete floors or embedded. All the CH pipework is under suspended floors leading on first and second floor, plus exposed in ceiling of cellar.

Problem started in April - noticed the boiler pressure had dropped to 0.6, but refilling loop was jammed. British Gas came out and changed it, refilled, etc - all fine.

CH turned off for summer, and no problems. 5 weeks ago, i turned the CH on and boiler started losing pressure again, topping up once every few days. I've had BG out 4 times now to check and they've done the following:

- replaced PRV
- inflated expansion vessel (apparently it was flat)

However, it seems that since the expansion vessel was pumped up, the pressure loss is now daily, going from 1.5 bars to 0.6 bars and off within 15 - 20 hours. it seems to hold a lot better when the heating is on (i.e. raising by approx 0.5 bar) but drops within a few hours when off.

I isolated the CH flow and return valves on the boiler 3 times overnight - pressure held in boiler, and decreased by at least 0.3 bar as soon as the valves were opened. This points to a leak in the system. However...

there is no water marks or signs of a leak on any of the ceilings, which i would expect such a large leak to create over a month-long period. Also, a leak detection company came out and confirmed this without charging me, which i was really grateful for. I've even had all the floorboards up in the one room which i thought could be the offender, but nothing.

I've checked all visible pipework for a leak, including radiator valves, bled radiators, even left whilte paper under then to see if this would identify any leaks - and nothing!

I'm at my wits end here - noone seems to know what the problem is - however, this is more than an inconvenience, as I'm aware that refilling the boiler every day is introducing oxygen into the system which is not good in the long term.

Any advice would be gratefully received. If it's not the boiler or the pipework, i really don't understand what else it could be!!

Title: Re: Daily boiler pressure loss - Help!
Post by CWatters on Dec 16^th, 2010, 5:25pm

Have you rechecked the expansion vessel/looked for signs of water coming out of the PRV?

Title: Re: Daily boiler pressure loss - Help!
Post by greg on Dec 16^th, 2010, 7:25pm

Try tying a bag over end or PRV pipe to see if anything is coming out?

Title: Re: Daily boiler pressure loss - Help!
Post by tomoose on Dec 16^th, 2010, 8:42pm

yeah, the PRV is fine - i've checked it a few times, and also had it replaced by BG. I haven't rechecked the expansion vessel yet - I've got my fingers crossed that it may be the diaphragm that's split in it - although all the signs so far are pointing to a problem with the pipework - and yet I can't find one!

I'm obviously worried that it's gonna end up being an expensive job - but i'm even more worried that, without ever finding the route cause, I may spend a lot of money on the wrong solution...

Title: Re: Daily boiler pressure loss - Help!
Post by cumbriahandyman on Dec 16^th, 2010, 9:03pm

It really is looking like a leak, you need to do a 100% check of all pipes under all floors.

Title: Re: Daily boiler pressure loss - Help!
Post by tomoose on Dec 16^th, 2010, 9:15pm

yep! In actual fact, if I found a leak I wouldn't mind as at least I would know what the solution would be, and it should be straightforward to fix. I'm just concerned that I can see absolutely no evidence of water leakage and am worried if I pull up the rest of the floor and find nothing I'll be non the wiser!

Worst case scenario I think would be that I'd be looking at having the CH system repiped. Does anyone have any rough idea how much this would cost? It's a 2 bedroom terraced house with 7 radiators - existing pipework is all under floorboards hence should be easily accessible once the boards are up. I've not found many sources online that can give me a rough idea - but don't imagine I'd be getting any change from £1000 - £1200 for a total repipe. Any ideas?

Title: Re: Daily boiler pressure loss - Help!
Post by greg on Dec 17^th, 2010, 7:36am

If you can not find source of leak then you can disconnect the boiler and rad valves, cap all ends and pressure test the pipework

Title: Re: Daily boiler pressure loss - Help!
Post by CWatters on Dec 17^th, 2010, 8:34am

What he said. Divide the system into sections where you can get access and pressure test each section.

Title: Re: Daily boiler pressure loss - Help!
Post by tomoose on Dec 19^th, 2010, 9:22pm

unfortunately, the system only has 1 isolator for the flow and return for CH at the boiler. Obviously, I could isolate each radiator - but I'm assuming that this literally isolates the radiator and not the actual pipework that leads up to it.

I'm assuming you mean isolating for example the upstairs and downstairs - which unfortunately I don't think my system has the capacity to do. If not, how do you mean 'pressure testing each section'?

Title: Re: Daily boiler pressure loss - Help!
Post by CWatters on Dec 19^th, 2010, 11:14pm

Yes seperate upstairs and downstairs. If necessary add isolation valves to allow you to narrow it down even further (eg to parts of the downstairs). That's going to be a lot easier than taking up entire floors on the off chance. You can allways replace the new isolation valves with couplings later if the valves are in visible areas.

Title: Re: Daily boiler pressure loss - Help!
Post by tomoose on Dec 20^th, 2010, 10:46am

thanks for the advice. From a novice point of view, is it quite simple to add isolation valves to the pipework? I'm a bit nervous about having to cut the pipes to fit them! is it best to leave this to an experienced plumber?

Title: Re: Daily boiler pressure loss - Help!
Post by cumbriahandyman on Dec 20^th, 2010, 12:10pm

http://www.youtube.com/watch?v=hPOlAN97mzg

Title: Re: Daily boiler pressure loss - Help!
Post by thescruff on Dec 20^th, 2010, 3:33pm

Just to add to Toms brilliant video.

The arrow simply points to the end that can be safely disconnected when the pipework is under pressure.

The leak is unlikely to be upstairs as it would show on the ceiling, so I would lift a couple of boards under each rad, where the pipes could get kicked, knocked with hovers etc.

You should find the boards are screwed down from when the system was installed and quite simple to get up.

Have you checked the condensate pipe, whether it is running when the boiler is off, could be an internal leak.

Title: Re: Daily boiler pressure loss - Help!
Post by tomoose on Dec 20^th, 2010, 6:18pm

thanks for the info - yep, the condensate pipe has been checked and is all fine. Literally everything has now bee checked in the boiler - so if's definately somewhere in the system.

Re: the leak unlikely to be upstairs - i'm kinda hoping it is as I've already had the floorboards up downstairs and found nothing!! With no signs of a leak appearing anywhere, I'm getting even more worried!!

Title: Re: Daily boiler pressure loss - Help!
Post by thescruff on Dec 20^th, 2010, 6:38pm

What is it pipes in plastic or copper pipe or a mixture of both.

Have you behind the rads and pipes with a mirror for any sign of staining.

Maybe stating the obvious but are you checking with everything cold..

What is the incoming mains pressure.

Title: Re: Daily boiler pressure loss - Help!
Post by greg on Dec 20^th, 2010, 10:55pm

If everything has been checked and convinced it is a pipework leak.

Drain system, isolate boiler with the boiler flow and return isolators.

Disconnect the radiator valve from the rad pipe tails, this will leave you with a nut and olive on the tail, use this to connect a ballofix to the rad tail. Do this to all of the rads except one, make sure all the ballofix are closed. On the rad you did not use the ballofix you can use the rad tail to connect the bucket pump. Pump up the system, go to each ballofix and open briefly to bleed out any air, re pump system. Leave under test, if after 1hr not dropped, then the problem is not with the pipework, suspect rad valves or rad bleed screws or rad themselves or something on the boiler. If test pressure does drop, then you can then split the system as per CW,repressurise and start tracing the pipes to find the leak or just repressurise and find the leak if you don't want to start cutting into the pipework, ballofix are quite restrictive so I wouldnt choose to leave them in once you've found the leak