Valliant Boiler keeps loosiing pressure

[mascia]

Hi can anyone help, i have a valliant combi boiler that keeps loosing pressure, i have change the safety valve as i thought it was this that was the problem but still the same thing is happening, i re pressurise the system but within a few hours it drops to 0 again. someone told me i might have to top up the air in the exspantion cylinder ? hope someone can help or advise what to try next

many thanks in advance

 

[Burnerman]

If you are constantly losing pressure then you have a leak somewhere.....if its not the pressure relief valve (PRV) then check all of the radiator valves for leakage.
If the expansion vessel has failed, then it will fill up with water, and then cause water to be forced outside.....I think your problem is deeper than that.
John

 

[mascia]

i have checked all rads but can not see a leak or feel any water, every time i put preasure to 1.5 bar and turn heating on preasure goes up and after about 1 hour prv leaks water and preasure goes to 0 again.. why it the preasure rising and activating the prv ?

 

[mascia]

i have checked all rads but can not see a leak or feel any water, every time i put preasure to 1.5 bar and turn heating on preasure goes up and after about 1 hour prv leaks water and preasure goes to 0 again.. why it the preasure rising and activating the prv ?

 

[MANDATE]

The Prv is set to open at 3bar. When you put the heating on watch, the pressure rise. It should go up by about 1bar.
From 1bar to 2bar or 1.5bar to 2.5bar is ideal.
If its reaching 3bar the PRV will discharge water and pressure will drop.
This is a clear indication of a expansion vessel problem.
Most likely lost it's air charge and instead of starting with a empty vessel it will be partially filled with water. This means there is less air than intended and compressing a smaller amount of air results in a much higher pressure.
Action is required to check/re charge but the vessel must be empty of water and system open to atmosphere to get rid of the excess water.
There is always a possibility the rubber diaphragm is 'holed' and water crosses from the water side to the air side.
Also there will be a flexible connecting pipe which could be partially blocked.
The bad news is that the PRV once opened may not close properly and make a perfect seal. So your still left with a small leak. The difference being that it takes longer for the pressure to drop 1bar.
So the two problems go hand in hand. Fix the expansion vessel problem first and then change the PRV

 

[Burnerman]

I suppose the important question is, how many times have you topped up, and how much water do you think you have introduced into the system?
John