Greenstar CDI, Pressure loss, not HE

[MartinDI]

I am a retired gas engineer. Corgi and Domestic Electrics + Building Surveyor. I have a Greenstar CDI 35kw that I fitted in my own home 15 years ago, serviced regularly, no issues till now. Suddenly its losing full pressure in approx 2 hours. I have concrete floors with buried copper pipe but when isolated, no leaks. No leaks anywhere else (air pressurised at 1.5 bar) that I can find either. So I assumed heat exchanger but no leaks through condenser, none anywhere else either and isolating boiler for 24 hours at 1.5 bar gives no loss. No PRV leak and I have changed AAV just in case, Pressure vessel reads 12 pounds and no fluctuations on the gauge. AAGH what's left. I have talked to Worcester engineering and they say definitely not HE but I am not so sure as little else left. Took inspection plate off, no water, flame burns normally, flue gas CO2/CO at correct ratio according to my Testo 325. Boiler runs perfectly otherwise. Its never run dry.

As it holds air with no problem it seems that the loss only occurs when its running. Condensate syphon had usual gunge but water only drips when boiler running. After switch off a minute amount from syphon for a few minutes then its bone dry. Some vapour from the flue but its freezing here and the anyway flame pattern seems fine nor is there any strange smell.

I would be really grateful for any help or suggestions. Has anybody seen these HE leak internally in a way that cannot be seen?

Thanks.

 

[Chuck]

If you have a vented DHW system then a leak in the cylinder coil might be to blame.

If the leak only occurs when hot water is circulating your isolation test may not be 100% reliable, so...

If you don't own one already, borrow or rent a thermal camera and have a look at the floors with pipes buried in them.

Try splitting the CH into two parts, e.g. upper and lower floor and run them separately. This will tell you quite a lot about where the problem lies.

 

[ShaunCorbs]

White or grey front ?

 

[MartinDI]

Thanks Chuck for the quick response I appreciate it. The system is un-vented totally sealed. I have in fact done what you suggest already and divided the system by floor. If there is any loss its tiny right across the carcass and the rads. It seems that the problem only occurs when the system is hot hence my thinking it has to be the HE. Next step I can fill and heat the top floor independently so that might show the fault, but I cannot do the same to the ground floor. My wife's freezing to death, even the dogs shivering, good thing I have a log burner as well. And Shaun its a a white front combi.