How can I fix my Potterton Netaheat 10/16 gas boiler?

I recently fitted a new water pump and when I turned the boiler on again it flared,died down flared died down and will not light properly. Nothing on or in the boiler was touched during its off period, which was about an hour. I've tested the air pressure switch which seems to be working ok. Do you think it's the thermocoupler? Regards. Sid