how can I fix amy glow warm boiler ultimate 50ff?

my problem is my boiler(glowwarm ultimate 50ff)has gone faulty during the christmas period due to a faulty fan.
I have replaced the fan but the bolier now wont start the fan is working ok the pilot is lit but the main burner is not coming on. I suspected the water pump but the pump found to be ok.
can you help me please0