Dettson
Underheating / Capacity or Control Issue
Boiler operates but house does not reach set temperature in cold weather
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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
Outdoor reset curve set too low, Undersized Dettson boiler, Heat loss greater than design, Circulator speed too low
How to Fix / Troubleshooting
Safety: Control adjustments should follow the Dettson manual.
- Check setpoints: Verify room thermostat and boiler supply temperature setpoints are appropriate for outdoor conditions.
- Adjust outdoor reset: If equipped, slightly increase the slope or shift of the outdoor reset curve to raise water temperature in cold weather.
- Verify pump speed: If using a multi-speed circulator, ensure it is not set to the lowest speed.
- Professional heat loss check: If the system still cannot maintain temperature, a contractor should perform a heat loss calculation and verify boiler sizing and distribution system design.
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Repair Difficulty
Medium
3/5
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