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we have a 12 month old Greenstar 30si boiler that has started to lose all its pressure very quickly. It is pressurized to 1 bar and after the central heating has been running for about an hour the system will lose all its pressure. We have checked for leaks on all the radiators and found none, there are no damp patches on the ceilings to indicate a burst pipe upstairs and we have checked and found no water coming from the pressure release value. The corgi plumber has filled the system with Sentinel Leak Sealer but this hasn't sorted the problem. When the central heating is off the pressure stays at one bar but when on drops after a period of running, usually about an hour but was 2 hours on one occasion. The only plumbing work we have done since the installation of the Greenstar was to remove and refit a bathroom radiator and towel rail in the upstairs bathroom. The radiators were all bled after the re-installation and there appear to be no leaks. The plumber is now concluding that the leak(s) is downstairs under the concrete flooring. The pipework has been there for about 30 years but seems to have been correctly protected. Before we go the the trouble and expense of replacing all the piping we were hoping that someone can suggest something we may have missed. To lose pressure so quickly it must be a big leak as we estimate that when repressurizing the boiler we have the 'tap' turned on for about 30 seconds. So a lot of water is going into the boiler and this must equal what is coming out but where is it going.

There's no water at all coming from pressure relief valve ?
If the pressure rises when the heating is on - it will discharge to outside, so there'll be alot of water coming out of the pressure relief valve for a few seconds that's all.

When the heating is on - heck the pressure gauge - if it's on 1.0bar when cold it should rise abit but no where near 3.0bar.

last evening before we switched the heating on we repressureised to 1 bar and switched the heating on. The highest the pressure got was 1.5 bar. As always it stayed at this level for a time - before dropping back to zero. At this point we switched the heating off. When we did so we heard a gurggling notice that seemed to be coming from the heat exchanger at the rear of the boiler.

Hello there -- we h ave EXACTLY the same problem that you have described and I wondered if you have any further help to offer ? We were thinking of getting one of these leak buster firms in to have a look, but am at a loss !! Any advice gratefully appreciated. Robert

Hi have you looked at the expansion vessel at the back of the boiler. There will be a car type inflation valve on it, at the top or bottom. Take of the valvecap and press the nipple, if water leaks out then you will require a new expansion vessel. If this is not the case then it is most likley the old pipe work

It's a pretty much brand new boiler and our plumber has been looking for the problem of course, I would hope that he has done this already, but I'll check .... thanks so much for your advice .... just loathe to start destroying new bathroom and flooring to try and find the leak ... has anyone had any experience with the leak finding companies -- this will be a last resort !! Thanks again, Robert.

I deal with bosch greenstars installed on the council contract and we have had problems with holes in the domestic hot water heat exchange plate pass this advice on to your heating engineer as he might not be aware of this, it is only because we have so many that I have come across this problem.
Otherwise I would have a hydroulic pressure test done with the boiler linked out.