Protherm
Control Logic / Demand Recognition Issue
Thermostat calls for heat but furnace starts with long delay or intermittently
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Possible Causes
Loose thermostat wiring at Protherm terminals, Faulty room thermostat or controller, PCB input fault, Anti‑cycle timer or frost protection mode active
How to Fix / Troubleshooting
Safety first: Turn off power before touching control wiring.
- Step 1 – Verify thermostat operation: Listen for relay clicks or display changes when adjusting setpoint.
- Step 2 – Check wiring: Tighten thermostat terminal screws at the furnace and 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 so, replace the thermostat or its cable.
- Step 4 – Control settings: Review Protherm control parameters for anti‑cycle times that may delay restart.
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Repair Difficulty
Easy
2/5
Required Part
Room Thermostat / Protherm Controller
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