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HomeRepair HelpThermal Zone Furnace RepairThermal Zone Furnace blower is running constantly but there is no heat Repair
Thermal Zone Furnace blower is running constantly but there is no heat
01 - Check Fault Codes
If the furnace stops working properly the control board will often display a fault code to help diagnose the problem. The fault codes are displayed by a flashing light or multiple lights on the control board. Each sequence of flashes followed by a pause will indicate either an error code or the status of the furnace. Some manufacturers will use red and green lights to indicate specific fault codes. Fault codes are often displayed on the access cover of the furnace for easy reference.
Common
02 - Thermal Zone Furnace Wall Thermostat
The wall thermostat has electrical contacts that control the power supply to the furnace. If the contact that controls the blower motor sticks closed, it will send continuous voltage to the blower motor, causing the motor to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the wall thermostat shows continuity between the (R) and (G) terminals when the thermostat is in the off position the thermostat has failed and will need to be replaced.
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Less Common
03 - Thermal Zone Furnace Wifi Thermostat
The WiFi thermostat has electrical contacts that control the power supply to the furnace. If the contact that controls the blower motor sticks closed, it will send continuous voltage to the blower motor, causing the motor to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the WiFi thermostat shows continuity between the (R) and (G) terminals when the thermostat is in the off position the thermostat has failed and will need to be replaced.
Less Common
04 - Thermostat Not Set Properly
Set the wall thermostat for "Heat" and set the fan for "Auto" or "Fan On". Set the temperature to be warmer than the room temperature. Keep in mind if the fan is set to "Fan On" the blower will run continuously whether the furnace is heating or not.
Less Common
05 - Fan Mode set to "Fan On"
The furnace blower will run continuously if the thermostat mode is set to “Fan On”. To prevent the blower from running continuously, set the fan mode to "Auto" or turn it off if heating or cooling is not required.
Less Common
06 - Thermal Zone Furnace Control Board
The control board has relays that regulate the voltage to each component in the furnace. If the relay that controls the blower motor fails while it is closed, it will send continuous voltage to the blower motor, causing the motor to run continuously. If the control board is at fault, replace it.
Less Common
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