Slant/Fin
Insufficient Heat Output / Underfiring
Boiler cycles on and off but thermostat never reaches set temperature
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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
Incorrect gas pressure (too low), Partially blocked burner on Slant/Fin boiler, Faulty gas valve, Incorrect boiler firing rate setup
How to Fix / Troubleshooting
Safety: Gas adjustments must be done by a licensed technician.
Homeowner checks:
- 1. Air filters and vents: Ensure baseboard covers and radiators are not blocked by furniture or dust.
- 2. Thermostat calibration: Compare thermostat reading to a known accurate thermometer; recalibrate or replace if inaccurate.
Technician tasks: A pro should measure manifold gas pressure, inspect and clean burners, and verify the boiler is set to the correct input per Slant/Fin specifications.
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Repair Difficulty
Hard
4/5
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