pottertonperforma 28 cutting out when running hot water (and doesn't re-light)

[deedgess]

Having changed the plate heat exchanger - problem persists. Boiler indicators climb to 60 deg - then 1 of 2 things happen: either the water runs cold (boiler goes out and doesn't re-ignite) OR when the tap / shower is turned off, the boiler fails to re-ignite, so the watere runs cold.

The boiler indicators show the temp at 60 deg (or are these warning lights for flame failure, safety thermostat, fault on fan/ flue AND fault on pump / low system pressure (wouldn't expect all these faults to appear at the same time, if they do, think i'll bin the boiler

If I leave the taps off until the boiler indicator drops to 50 deg, then turn the tap on, hey presto, the boiler fires up - and so the cycle continues. - Any ideas ?

 

[deedgess]

AHA - the proble seems to be with the pressure differential valve - for some reason, it operates correctly when the hot water is first called for, but then the piston retracts and isn't coming out to play until the temperature reduces to below 50 deg - suspect valve diaphragm ? - or is a sensor somewhere causing the problem?

 

[deedgess]

UpDATE: changed the PDV - now have continuous hot water