I have a nine year old Baxi 105e that is responding to calls for DHW and CH, but will not go to secondary ignition, so it only heats to like warm temperatures. So far, I have bridged out the CH thermistor, taken out the fan, airbox and gas burners and cleaned them. I have also checked the flue for obstructions and the air switch sensore tubes for damage. I've also taken the diaphragm out to check for damage. No luck. Any ideas that don't involve a new PCB?