Thermostat calls for heat, but the furnace starts with a long delay or intermittently.

Safety first: Turn off power before touching control wiring.

• Step 1 – Verify thermostat operation: Listen for relay clicks or display changes when adjusting the setpoint.
• Step 2 – Check wiring: Tighten thermostat terminal screws at both the furnace and the thermostat.
• Step 3 – Bypass test: For simple on/off thermostats, briefly bridge the demand terminals at the furnace to see if it starts reliably. If it does, replace the thermostat or its cable.
• Step 4 – Control settings: Review Protherm control parameters for anti-cycle times that may delay a restart.