Dettson
Overheating / High Limit Cycling
Dettson furnace short cycles: starts, runs for a few minutes, then shuts off before reaching thermostat setpoint.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Dirty or restrictive air filter, Blocked supply or return ducts, Undersized ductwork for furnace output, Weak blower motor or incorrect speed tap
How to Fix / Troubleshooting
Safety first: Turn off power before removing panels or reaching into the blower compartment.
- 1. Replace air filter: Install a new filter of the correct size and recommended MERV rating. Avoid overly restrictive high-MERV filters unless ductwork is designed for them.
- 2. Check registers and returns: Open all supply registers and return grilles. Remove obstructions like furniture or rugs.
- 3. Inspect blower wheel: Remove the blower door and check for dust buildup on the wheel. Clean carefully with a brush and vacuum.
- 4. Verify blower speed (advanced): On PSC motors, ensure the correct speed tap is connected for heating per the wiring diagram. On ECM motors, configuration may require a technician.
- 5. Monitor operation: After improving airflow, run the furnace and see if it maintains longer cycles and reaches setpoint.
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Repair Difficulty
Medium
3/5
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