Double check the integrity of the electrical connections you've disturbed - just in case you've fixed it without realising it!
When the boiler gets a call for heat the fan is started - a pressure switch senses the correct pressures in the sealed unit and signals the control electronics. The PCB causes the pilot electrode to spark and opens the pilot gas valve. A heat sensor monitors the heat of the pilot flame and signals the control board which opens the main gas valve and the boiler fires up. If the pilot fails to ignite the fault may be fan, case seals, flue, pressure switch, PCB (not recognising pressure switch, failing to make spark or failing to open pilot gas valve) or the pilot gas valve not operating.
If the pilot flame does light but the boiler not fire up the fault may be: pilot flame too feeble to properly signal control board, heat sensor not working, PCB not recognising or acting on signal from heat sensor, and most often, main gas valve not working.
Good luck...
Peccavi, June 2009
