Vaillant VCW-Sine 18 T3W Loss of pressure

[Kensal]

I have had the Vaillant combi installed since 1985 and I have been very pleased with its performance but now have a problem.
I need to pressurise the system at least once per week. I pressurise it to 1.4 bar, and within 3-4 days the pressure has dropped to approx 0.4 bar or lower.
I have checked all the radiators and can find no evidence of any leaks.
Can anyone help please?.

 

[LUNAT]

HI

Does the water leak from prv ?

 

[Kensal]

Thanks for the reply, but I have not seen any discharge from the prv.

 

[LUNAT]

HI

check expansion vessel for correct charge about 1 bar when system empty.

 

[Gasman28]

Could be a leak on the CH system under the floorboards?

 

[Agile]

Behind the pump a bit to the right is the AAV.

These often leak !

It only needs a little wetness to need repressurising every week.

You could just close the cap or get it replaced.

Tony

 

[Kensal]

Could be a leak on the CH system under the floorboards?

Thanks for the suggestion. I don't think it is this as I have no evidence of a wet patch in the ceiling when looking up from the ground floor.
I must admit I cannot check under the floorboards on the ground floor without taking up all the carpets. The pipes under the ground floor have not been disturbed since they were installed. The drop in the pressure has only been the last few years, so there was no leak from underfloor pipes for at least 23 years.

 

[Gasman28]

'The drop in the pressure has only been the last few years, so there was no leak from underfloor pipes for at least 23 years.'

That doesn't mean to say that there isn't one now.
You could try injecting a leak sealer into your system, such as Fernox F4 to see if this cures your problem. If not, you will have to investigate further - if that means taking up the carpet/floorboards to solve, then I'm afraid that has to be it.

 

[Agile]

Behind the pump a bit to the right is the AAV.

These often leak !

It only needs a little wetness to need repressurising every week.

You could just close the cap or get it replaced.

Tony