Thanks guys for the info provided so far. I bought a new pump overun stat and got a local boiler man to fit it as he thought it was more than likely that.
But it still happens.
If I run the boiler on 3 its perfetly ok, if I increase it to 3.5 it starts locking out INTERMITTENTLY.
When the room temp is reached the boiler shuts down as normal but the pump stops straight away, then the boiler locks out after a short time.
I wonder if it a bad connection aggravated by heat and note that it has a PCB.
Any ideas?
Gerry

Gerry, January 2010

i generally replace the 3 stats (pump overrun, boiler stat & overheat stat) on these boilers if having this problem & never had any trouble with the fault re-occuring after doing it so far. you need to make sure burner pressures and circulation is ok.

Ian, January 2010