Potterton Suprima 40L - always on

[Peter Brown]

Hi
I am not totally convinced it is the PCB at fault.
The heating and hot water started running continuously on Sunday, only way to stop was to switch off mains power.
I have checked room thermostat and it switches over when up to temperature so not that. Checked programmer and it appears to work, in fact ran boiler with both room thermostat and programmer removed and boiler fired up quite happily.
So, do I change pcb again? This is new version as I replaced original back in 2011. Or is there something I am missing?

 

[ianmcd]

its not the pcb, if you have an S plan one of the end switches is sticking on one of the zone valves, if you have a Y plan the 3 port valve is faulty

 

[Peter Brown]

Not sure about S or Y plan.
I have 2 divertor valves, one for CH and one for HW.
Assume it is likely to be CH one?

 

[ianmcd]

that is an s plan , could be either valve, turn off heating and hw and see if both valves return, there is a lever on the side of the valves when on, the lever should have no resistance, when off you should have to add pressure to manually open the valve,if either valve offers no resistance when turned off the fault is the actuator has seized,if they are both operating correctly you will need a multi meter

 

[Peter Brown]

Hi
Yes, it was CH valve. It was stuck, couple of taps on coil and it sprung back and working again.
Thanks for helping.