Grant
Under-Firing or Heat Loss
Boiler’s burner runs continuously without reaching set temperature, system slow to heat.
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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 nozzle size (too small), Low oil pressure, Partially blocked heat exchanger, Excessive system heat loss or undersized radiators
How to Fix / Troubleshooting
Safety: No immediate hazard, but efficiency is reduced.
User checks:
- Ensure all doors and windows are closed when heating is on to reduce heat loss.
Engineer actions:
- Verify the nozzle size and type match Grant’s specification for the boiler model.
- Measure and adjust oil pump pressure to correct value.
- Inspect and clean the primary heat exchanger and flueways.
- Assess system design for heat loss and radiator sizing.
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Repair Difficulty
Hard
4/5
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