More boiler woes but a separate issue from the condensing pipe.
Topped the pressure up yesterday as it seemed rather low, heating came on this morning and once it had turned off I rechecked the pressure and it was right down again to 0.5bar (any lower than 0.5bar and the heating won't come on)
No signs of any leaks from the boiler or the CH system and given how quickly the pressure had dropped, signs of a leak would be pretty evident so suspicions quickly turned to the expansion vessel and or the prv (pressure relief valve)
On old school open vented systems with a hot water cylinder and f&e (feed and expansion) tank, expansion in the system when heated is taken up in the f&e tank, on a combi boiler sealed system there's an expansion vessel with an inflated rubber bladder inside, when the bladder is flat or pierced there's no room in the system to take up the expansion so when the heating comes on and the system pressure rises and goes over 2.5bar the prv opens and dumps CH water out the discharge pipe, then with the combination of the system cooling and the loss of pressure/water via the discharge pipe, the system pressure will be low, often too low for the boiler to operate (sub 0.5bar on this boiler)
Went to check the expansion vessel pressure which should be about 11psi and water came out the schrader valve not air π Problem found.
On Ebay there are listings for the expansion vessel and a new prv, there might not be a problem with my prv but under normal circumstances they never open, when they do (pressure goes over 2.5bar) they open up as CH water is discharged and then close again but CH water often contains bits of crud and debris even when the system has been ran with inhibitor, so when the valve snaps shut again it doesn't always make a pressure tight seal which is no good for a sealed system. Parts ordered.

















