Central heating system keeps losing pressure, can't find a leak

[WillFuller]

Hi all,

New to this forum. Wonder if anyone can help. I have a Worcester Bosch Greenstar 37CDi combi in a 4 bed detached house, fitted with new radiators two and a half years ago. The house is about 30 years old. Since December I'm constantly finding the pressure in the central heating circuit is dropping. I assumed there was a leak, but we've had plumbers round for hours checking under the house (full access under all downstairs floors), under the floorboards and round all the radiators and there's no sign of any water escaping anywhere.

I'm now at the point that if I charge the system up to 1.5 bar, then it needs recharging the next day (i.e. almost 0 bar), and I'm also bleeding loads of air out of the top floor radiators - so there's masses of water getting out somewhere. Because this is a fairly new house we have good access under all floors and we can see that there's no sign of water damage anywhere. We've checked the pressure release valve on the outside of the house isn't letting anything out. My plumbers (who are Worcester Bosch approved fitters) have never seen anything like it and really don't know what the cause is. The only option they can think of is that the heat exchanger is cracked / leaking. Any other suggestions out there?

Thanks for looking

 

[Puddle]

Just about to suggest it and you mentioned it in the last line,main heat exchanger split,had about 6 of them,so not uncommon,check condensate pipe when boiler not in use,see if still dripping ,however usually becomes visible around heat exchanger base

 

[alidd33]

I had a similar problem with losing pressure on my sytem, had a succession of plumbers and heating engineers tell me the system was leaking somewhere, they would then duly top the system up one and all...once I'd read up on the subject I found out all it was, was the expansion vessel needed recharging properly. It amazes me they were all qualified people yet I had to do the job properly myself, but I must admit I get a great sense of satisfation in that I fixed it! of course

 

[WillFuller]

Thanks for the comments. My plumber will be back from a course next week. While I wait a couple more questions:

I charged to 1.5 bar when the system was cold last night and the pressure had dropped below 1 bar before it fired again this morning. Does this rule out the expansion vessel (losing pressure over ~7 hours while off all that time)? Is there an easy way for me to check if the expansion vessel needs charging (no technical know-how here - boiler is a white box that hangs on the wall as far as I'm concerned)?

I know the hear exchanger is guaranteed for 10 years. In practice are Worcester Bosch quibble-free when it comes to replacing these? Are they going to pay for the labour as well as the part - and what about the time we've wasted so far investigating this problem? We had to rule out the leak being elsewhere in the system first of course so in the end this is going to end up costing me several hours time to investigate.

Thanks again

 

[GrahamM]

You say the pressure relief valve pipe termination outside has no indication of water coming out. If you are sure of this then this should rule out the expansion vessel or pressure relief valve being faulty.
You sure there is complete access to all pipework and this has been checked?

 

[WillFuller]

I've had a plastic bag tied round the pressure relief bag since before Christmas and its still dry. Sometimes a couple of the upstairs radiators are completely full of air - so we're losing plenty of water and I think we'd see evidence of this if it was inside the house since this has been going on for more than 6 weeks now. The sleeper walls under the house are knocked through so should allow access throughout the under house area. I haven't gone down there myself but the plumbers were at the house for 2 hours on Weds and they report that its completely dry down there, and they couldn't find any problems with any radiators.

I do sometimes hear trickling coming from the condensate pipe coming from the boiler. It's locked onto another waste pipe (but I take it if I want to be sure the heat exchanger is cracked we'll need to detach it and see what runs out?). Sometimes this is when the boiler isn't running (although will it still trickle when the boiler was running recently?). Often when the system is running one of the downstairs radiators sounds a bit 'fizzy' - like there's air and water mixing in it.

Thanks for your help

 

[davebigpipes]

Tea the condensate pipe shouldn't trickle at all when off even if its been on recently

 

[GQuigley67]

you can turn boiler off, disconnect condensate waste pipe and put it into a bucket, if the bucket fills up H.E has split

 

[BigBuilder1]

Hi, new to this so apologies if I've hijacked the thread but this is so similar to what I'm experiencing - even down to the same, but higher capacity, boiler and manufacturer.
As Will's stated I can also get every joint in the system and every one is dry but I'm still losing pressure - although, not at the same rate as Will. I'll certainly check the points raised by previous advisors but, I'm wondering: is there a tracer dye you can introduce into the system via, I have a MagnaClean, to try and see where the water's coming from ?

 

[FD Powerflow]

Not much point putting a dye tracer in BigBuilder if you cant find any water anywhere, mostly used on GSHP loops etc. Try hiring a thermal imaging camera from your local HSS, get the boiler on full heating load, then get the camera out and trace any pipe runs your not able to access, if theres a large spread of heat, it could be down to a leak. You could also try a can of F4 Express, open up the magnaclean and squirt it in, run the boiler up to full temp which will seal any micro leaks. Also worth calling the Worcester technical line, great guys and girls in their, with boilers on the wall to help explain what could be going wrong, you will need your GSR number.

 

[bewsh]

Isolate the boiler, if it still drops then its an issue with the boiler, if it doesnt, then it's an issue with the system

 

[BigBuilder1]

Thanks very much for this good advice, people.
I'm not GSR - far too expensive ! Contacting Worcester is a good idea.

Would be interesting if Will could let us know what his problem was and whether he managed to sort it as it could be relevant to me.

 

[Dotty]

Contact either Worcester or a local gsr. I'm afraid that's all the advice we can safely give you.