Potterton Netaheat Profile 80e?

The boiler will not fire up when heat is called for. The pilot lights up and remains on with the fan working as normal.

I have looked at the fault finding chart and it says " check solenoid GV2, replace if necessary". I take it that this means the Gas Valve. How does one check this?

Another possible option is that the air pressure switch or the tubes to and from it are faulty. How does one check the switch?

Am I on the right track