Pressure drop in Biasi combi boiler

[fb36]

Hi

Sorry another query about pressure drop in a combi boiler.

The boiler is a Biasi 28S combi. The pressure will drop only after the central heating has been on but if I re-fill and leave the heating off, the pressure does not fall. Incidentally even if the pressure has dropped right down to zero there is no loss of heating or hot water. Everything appears to work just fine still. Is that unusual ?

Have checked for leaks at all the radiators and can find none, they have all been bled and are all hot top and bottom. The boiler itself has been checked over by engineer who says it is in perfect working order.

Before I contemplate taking up floor boards to look for leaks I just wondered if the fact that the pressure does not drop when CH is off might point to the the problem not actually being due to a leak.

Would be grateful for any advice. Thanks

 

[gas4you]

When its on for ch what pressure does the gauge rise to and does it rise very quickly?

Possibly expansion vessel needs re-pressurising or replacing if rise is quickly to 3 Bar +.

Search on here for re-pressurising the expansion vessel.

 

[fb36]

Pressure rises quickly to about 2.6 - I've not seen it go over 3.

Will look into re-pressurising expansion vessel.

Thanks

 

[Agile]

Have you been checking the PRV vent for any discharge?

Tony

 

[fb36]

yes I can feel some water discharge at the PRV but not much - a few drops really

 

[Agile]

Put a bottle over it and see what the daily discharge is!

Its not meant to drip at all !

Tony

 

[fb36]

Hmmm I stand corrected, not a few drops - 350mls over 24hrs.
The CH was on for the last 3 of those hours. All this water was discharged during the time the CH was on.

The pressure unsurprisingly is now back at zero.

 

[Agile]

Well as you have been advised the expansion vessel if faulty or flat.

See FAQ for details.

Tony

 

[ChrisR]

the pressure is lost during CH operation because there's so much more water expanding (outside!) then.

 

[fb36]

I'll get that fixed then.

Thankyou so much all

 

[SBRD]

I had the same boiler and mine was doing exactly the same thing, all I did was re-pressurise the boilers expansion vessel with 15 pumps on a bike pump. There is a connection point at the top rear of the boiler...