PCB? Or something else?

[Tightbarsteward]

We've got a Potterton Suprima 40 that seems to be acting up. At the moment the problem is intermittent, but it's slowly getting worse.

Most of the time the system works fine, but on some days the boiler gets into a state where it is receiving a request from the cylinder for more heat (flashing green light) but seems to think that the target temperature has been reached (steady red light) even though the water coming out of the taps is luke warm at best. In other words, it's being told to fire up by the cylinder, but it's not doing it because it thinks the water is hot enough. When it's in this state, pressing reset does zilch, but cutting then restoring the power to the heating system brings it back to its senses , the boiler fires up and all is well for another day or two.

At first I was thinking faulty thermostat, but if that's the problem, how come a power reset fixes it for a time? Could this be a symptom of a failing PCB?

Any ideas, fault-finding procedures would be greatly appreciated.

 

[corgiman]

Pound will get you a penny it is the PCB mate. It always is

 

[ChrisR]

The classic needtokeepswitchingitoffandon Suprima pcb problem. Can sell you one well below trade - anotherletterboxATaol.com . Use the @ symbol.