In message , MP
writes
Hi there.

Well, my boiler isn't firing up for hot water or heating!!

What I know is :-

1. The boiler pump works
2. The system pump works
3. The 3-way electric switch works (and I've just changed the motor).

Having read the other posts now and established what boiler it is

really you need a meter to test for mains

I think that your boiler uses a 309S376 pcb

The pins on the pcb are marked as to their function and you should be
able to diagnose a fair bit from testing the voltages on the various
pins

First check that there is mains going onto the pcb, if so, pull the
connector off which is marked O/H and test whether it is a short
circuit, if not your overheat stat has tripped

If it is a short circuit, then check that you have 240 volts to the fan
(which you should if the o/h stat is OK). If you do, check to see if the
fan is rotating, if not, then either the air pressure switch contract
resistance has gone high or the fan is knackered.

Remove the connector and check to see if the fan is open circuit or has
a finite resistance (I think 50-100 ohms).

Does the fan rotate freely or is it stiff ?

That's enough to get you started


--
geoff