Vokera Compact 28 - Constantly Going To Red Light

[stewhi]

I have Vokera compact 28 appox. 4 years old.
When central heating is on the boiler will sometimes run ok for days and other times constantly go to red light which renders the boiler useless. This does this at whatever water temp. the central heating system is set to on the boiler itself.
I have recently had the hot water thermostat changes because water temp. was eratic, with hot water not constant at all, the new thermostat solved that.
Any ideas with the central heating problem??
Could it be main PCB thats at fault, or is there a thermostat pcb??
Thanks for any help

[Henry]

with that boiler as with many you change all the sensors and stats never 1 also check the fan switch is resetting.

[stewhi]

Thanks for your reply.
much appreciated
cheers