If an electric furnace stops working when the thermostat is turned on but works fine otherwise, there could be a few potential reasons for this issue:
Thermostat Malfunction: The most common cause of this problem is a malfunctioning thermostat. When you turn on the thermostat, it sends a signal to the furnace to start heating. If the thermostat is not functioning correctly, it may not be sending the signal to the furnace, resulting in no heat being produced.
Wiring Issues: There might be an issue with the wiring between the thermostat and the furnace. Faulty or loose connections can prevent the thermostat's signal from reaching the furnace properly.
Tripped Circuit Breaker: If the furnace is drawing too much power when the thermostat is turned on, it could trip the circuit breaker that supplies electricity to the furnace. This would cut off power to the furnace and prevent it from working.
High Limit Switch Activation: Electric furnaces have a high limit switch as a safety feature. This switch shuts off the furnace if it detects overheating. If the furnace heats up too quickly or there is an airflow issue (e.g., dirty air filter), the high limit switch might activate and turn off the furnace when the thermostat calls for heat.
Sequencer or Relay Issues: Electric furnaces often use sequencers or relays to control the heating elements. If one of these components is faulty, the furnace may not respond to the thermostat's signal.
Blower Motor Problems: If the blower motor responsible for distributing the heated air is malfunctioning, the furnace might not start when the thermostat is turned on.
Thermal Cutoff Switch Triggered: Some furnaces have thermal cutoff switches that shut down the unit if it detects an unsafe condition, such as overheating. If this switch is triggered, the furnace won't operate.
It's important to note that electric furnaces can be potentially dangerous to diagnose and repair if you're not familiar with electrical systems. It's best to seek the assistance of a qualified HVAC technician to diagnose and fix the issue. They have the expertise and equipment to safely troubleshoot the problem and carry out any necessary repairs. Avoid attempting any repairs yourself to prevent personal injury or damage to the furnace.