Once the pilot light is alight the main gas valve should open to fire up the boiler...
The fault could be:
Weak and feeble pilot flame (partially blocked injector) not providing enough heat to make the sensor work properly.
Sensor that monitors the pilot flame heat defective.
Control board not "seeing", or acting upon signal from pilot heat sensor and failing to open the main gas valve.
Main gas valve defective and not opening when "called" by control board.
The first thing the engineer should check when he arrives is the power to the main gas valve - if the control board is asking it to open and it is not doing so it will need to be replaced £££.
If the engineer claims, "it's the control board", he may be absolutely right but ask him what he intends with respect to costs if he is wrong. ££
If you get it fixed for under £200 you will have done well.
Peccavi, May 2009
