Valliant Boiler

Belenus

You may have a leaking valve in the boiler's internal expansion vessel.

We had a similar pressure drop problem. It transpired that the Schrader valve (as used in most bicycle tyres) in the expansion vessel was leaking slightly.

A new valve and topping up the pressure in the expansion vessel fixed the pressure drop issue.

Your problem may be different.

Newcad

Le_Kirk said:I am not sure that expansion vessels are filled with nitrogen.

It depends on the vessel, but agreed that most domestic boilers simply use compressed air.
Nitrogen is more used for larger vessels/boilers for communal heating systems, and TBH I was thinking of the boiler we used to have when I lived in a hotel.

Just another thought;
Rather than a leak on the piping it could be that the pressure relief valve after being in use when the old vessel failed is now no longer sealing properly or even not fully closing.
We can conjecture all we like but in the nend it needs someone to take a good look at the boiler/system.

lazydave

I had a similar issue with regular pressure drop.  Called a heating engineer friend and he suggest that before I panic and call someone out I check the carpets around my radiator pipes in case a pipe had been knocked and was leaking.  Sure enough that's what it was.   May be worth 5 minutes before you pay callout?  Good luck with it whatever it turns out to be