ferroli modena 80e fault

[simonfisher2312]

On both DHW and CH the boiler fires up and after a few seconds it turns itself off, then it fires up again and repeats this process, it does not bring up the lockout light.
any help would get me some brownie points with the mother in law.

many thanks

 

[ollski]

could be the fan, gas valve, electrodes, gas meter, pcb, air pressure switch...but I usually go for the sensors first and it normally is.

 

[simonfisher2312]

I might try flame detector sensor first, then pcb. fan and pump seem to be working fine. If it was one of the temp sensors, then surely the boiler would not fire up at all or stay on permanently.
If I disconnect one leg of the temp sensors will this fool the pcb into thinking that the water in system is cold, i will not short them out as some pcb do not like this.

thanks for help so far

 

[Gasguru]

I might try ............, then pcb.

Not so fast...you can't just change the pcb, it requires setting up by a corgi..gas burner pressures etc.

 

[superdupergasman]

thermistors give the correct reading then go out of range as the temperature in the boiler rises...hence cutting on and off..... I would go for the termisors first.....try swapping the wires round from DHW to CH and vise verca...if it fires on CH then you can prove the faulty sensor.