RAVENHEAT CSI 85

Boiler was not responding to either of the hot water or htg boiler stats,consequently it was overheating and blowing the prv and going off on high limit.
On advise i changed the micro switch on diverter valve and checked all electrical connections, unfortunately same thing happened.
I've dissconnected both thermistor connections and the boiler is still coming on. ITS ALIVE ALIVE.
Im of the opinion the pcb is the only thing left, can anyone put me out of my misery pleeeeaaasssseee.
ps the neon doesn't come on when boiler fires up and i know it does work.

sarahs dad said:

Boiler was not responding to either of the hot water or htg boiler stats,consequently it was overheating
On advise i changed the micro switch on diverter valve

Click to expand...

whaaaa?? how can it overheat if there is no response? Something must be making it fire up.

Sorry I have no experience of Ravenheats but if you disconnect thermister leeds most pcb's would not allow the boiler to fire, so this alone is a real worry.

You do need specialised help.

with the thermistor leads on in their rightful place disconnect the microswitch head. Does the boiler still light when there is no call for heating?
I suspect that the pin is stuck out on the diverter valve operating the microswitch which then calls for DHW and lights the boiler .
Inside the diverter valve there is a diaphragm which could need renewing.
It is possible that the return spring has snapped. Maybe the diaphragm has been renewed and not fitted correctly.
Otherwise we need to figure out why the pin is not going back in.

Can you give any more background info ?
How old is the boiler?
When did the problem start?
What was the last work that was done on the boiler and when [before the microswitch]?
What is the pressure prior to turning the boiler on?