Hi,
I recently moved house and my Potterton Profile 100e is playing up. The previous owners told me that they had replaced the pcb and the gas valve. The old gas valve is still in the garage and I notice they have switched from a S.I.T valve to a White Rogers. I’ve checked to see that the Pilot is not blocked and it isn’t.
When I turn the boiler on I can hear the fan come on, an audible click of the pressure switch and a faint metallic clunk, which I guess is the gas valve.
The electrode is sparking away but there is no pilot light. The seals to the front cover are also new.
Has anyone got any suggestions how I can diagnose the fault by a few simple tests/checks?

A standing and running pressure check at the gas valve would determine if gas is actually reaching the valve or if any gas is passing through.

You could do the test yourself,  but seeing as you don't even know what equipment to use (it's a manometer by the way), I seriously recommend you seek professional help.

The fact that the ignition is sparking suggests to me that the boiler has already got to the stage where it's trying to fire up but there's no gas there to ignite. This is only natural assumption and there could be many other reasons why it's not working.

I'm sure this doesn't apply to you, but I once looked at a boiler with the same problem and it turned out to be the meter needed another 50p in the slot. In all fairness the tenant had only lived there for a few weeks, but you get the picture  

Trust me, I am handy at most things and I if you think that I could do the test safely just tell me where to place the manometer and what to look for. By the way, the gas is turned on and we don't have a coin meter thingy. (It's off at the moment)
Is there a simple way to eliminate the pcb and pressure switch  before concerning myself with the gas valve, other than just by sounds and sight?