Substantial loss of pressure in central heating system

[Lionel12]

The pressure in my central heating system drops very fast (at the rate of 1 bar every 3 or 4 days), which requires me to top it up. The rate of loss seems to be higher when the heating is on for longer periods of time. I have checked my installation and cannot seem to locate a leak on pipes, rads or valves. And I suspect that considering the size of the leak I should notice it over time. I have also checked the pressure release valve and I believe that it is not leaking

Could the loss of pressure result from the boiler?

I have a 10 year old combi boiler (Vaillant).

 

[twgas]

try tying a plastic bag over the PRV discharge pipe to confirm its integrity one way or the other.

 

[homerj]

your expansion vessel may be burst or need repressurised, this would result in water coming out your pressure relief valve though, check too see if water comes out off the air valve at the top off the expansion vessel

 

[Lionel12]

Thanks for those tips. I will check next week. I have an early version of the condensing boiler. I have noticed that a certain amount off water comes out off the condensate pipe. Can this mean anything?

Thanks
lionelH