Combi boiler keeps filling

[WaterWorks1]

Hi

I have a Halstead Finest Gold Combi Boiler haven't had the central heating on for about 7 months and the hot water has been fine.

Now when the central heating comes on the pressure gauge rises and the blow off activates at approx 3bar.

I initially thought that it would be a faulty expansion vessell or PRV but the system keeps filling up so water is getting in from somewhere when the c'h is turned on.


Does this mean it is filling through the diverter valve and if so can it be changes easily and whats cost should it be?

Any assitance much appreciated

Cheers

 

[rojaca]

expansion vessel lost charge or split
prv will need cleaning or replacing
Fliing loop should be removed after filling
Diverter isn't involved

 

[kevplumb]

agreed rojaca


the only time its filling is when you top it up

its not coping with the expansion of the water when heated

 

[OilLecky]

I'm not a plumber but I do service oil boilers. Is your filling loop turned on? I think that it is the only place that your system can fill from. It is normally a flexible pipe with a valve at each end, the one on the boiler end being an NRV. They should both be off. (and really the loop should be disconnected.
Locate the filling loop and turn it off. Drop the pressure to zero using the safety valve ( the one that is "blowing" the water out.) make sure that the expansion vessel is empty. If not carefully empty it into a bowl. When the expansion vessel is empty depress the schrader valve and see if black water runs out. A little is OK but a lot means that the diaphram is bust and you need a new vessel. Check the air pressure in the vessel using a tyre pressure gauge. Sometimes 0.5 bar sometimes 1.0 bar. But make sure that you have pressure. (This is the area that the water will expand into when it gets hot.)
If your Exppnsion vessel will not hold air or if black water runs out change it for a new one. Good luck.

 

[OilLecky]

Waterworks,
Sorry, as I was writing my suggestion I got a call out to a, not disimilar problem to yours and got interrupted.
I forgot to tell you that once you had the correct air pressure in the expansion vessel, as shown on your tyre pressure gauge, and you had reconnected everything, you then refill the water system. This is done by opening the filling loop valves until the pressure gauge pointer aligns with the red pointer. You then turn off the valves and you should disconnect the filling loop.