Pressure slowly dropping in sealed system

[cholma]

Hi - first post, so please excuse if this is done to death elsewhere ...

We've recently moved into a house which has a 9 (?) year old Alpha SY24 system boiler. Given the marks below the vent pipe outside, it's obviously had some issues for a while. From the way that the pressure rapidly rises to 3 bar (25-30 mins of central heating coming on), we seem to have a problem with the expansion vessel. We've been nursin it along so that it doesn't vent too much water, but this will soon become an issue as we enter Winter.

Considering at the moment whether to just get an external vessel fitted, or replace with a new boiler.

Anywho ... my question is regarding the pressure. I last topped it up about 10 days or so ago, to 1 bar. Since then, it's vented a bit of water a few times (to my knowledge), and the pressure has gradually dropped (when cold) to around 0.4 bar. I've been quite careful with checking the vent pipe, so I believe that it's only vented a few times.

I've found that one of the radiator TRV valves is weeping water, even after I tightened it up. Would a relatively mild weeping (gets some tissue underneath damp, but not soaking) account for a drop of maybe 0.07-0.1 bar per day ? There's no apparent water leaking in the boiler, and no other leaking from radiator valves, so my main concern is that there isn't leaking elsewhere in the system.

 

[ismellgas]

could be a combination of venting a little, radiator weeping a little and possibly heat exchanger weeping a little aswell, but drying up before it leaves chamber.. I've seen it before..

 

[RoyMacDonald]

If your pressure relief valve has released water it needs replacing. They have a knife edge seal that is incredibly easily damaged if it passes water for any reason.

I had the same symptoms you describe after my system installer's maintainance guy drained the system using the relief valve. It took the companies system designer to identify the problem.

 

[45yearsagasman]

The mention of pressure rising to 3 bar would point me in the direction of the exp vessel.This needs to be checked for its charge pressure.Depressurise your system(not via PRV) and find the exp vessel schraeder valve and using a car tyre pump with a fitted guage,connect to the valve and check precharge.Should be approx .8-1 bar.If water comes out of schraeder then exp vessel is caput.If pressure is low then pump it up.Refill system and remove all air and give it a test run.Another reason maybe the connection pipe to the exp vessel may be blocked.This is easily repaired.I hope you have the DIY skills to attemt this work.

 

[cholma]

Thanks for your responses.

As a few things need doing in the house, I'm probably going to take the route of ading an external expansion vessel, but I'll definitely ask the engineer to check the pressure relief valve - although I'm pretty certain that he mentioned it didn't show signs of damage when he re-pressurised the expansion vessel.

I'm not really a DIY person - painting is really the limits of my competency. Playing around with water systems would stress me out WAY too much.