A proving switch appears to stop ignition
A furnace receives a heat call and starts its inducer, but the ignition sequence stops before the burner fires. The service manual identifies an air-proving condition that must be established before ignition. A previous worker has suggested permanently jumping the switch because the inducer can be heard running. The current technician finds a deteriorated signal hose and notes that the intake and vent have not yet been inspected. The switch’s actual differential, contact state and specified replacement characteristics have not been checked. The appliance is being held out of normal operation while the technician plans a systematic diagnosis. Both electrical and gas isolation procedures are available for the required inspection.
1. How should the technician distinguish a failed switch from a correct protective response?
Read the worked answer
Follow the specified sequence and test the actual pressure signal, hose condition, switch state and airflow path using suitable instruments. An operating motor sound does not prove that the required airflow or pressure condition exists at the switch.
2. Why must the proposed permanent jumper be rejected?
Read the worked answer
It would bypass the proving function and could allow ignition despite an unresolved airflow or venting fault. Correct the underlying condition, use only the specified compatible parts and verify the complete affected sequence before return to service.