Dunkirk Error E12: Casting
The cast-iron heat-exchanger casting temperature limit switch opened, indicating the block got too hot or air is trapped at the top of the casting. The control enters hard lockout. Display shows 'E12'; manual RESET required. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
The cast-iron heat-exchanger casting temperature limit switch opened, indicating the block got too hot or air is trapped at the top of the casting. The control enters hard lockout. Display shows 'E12'; manual RESET required.
Dunkirk fault codes can vary by model and series. Use this as a guide — the same code can have more than one cause. Our Technical Safety BC–licensed technicians read the code, confirm it against your unit's manual, and diagnose the true cause before any repair.
Likely causes of Dunkirk error E12
- Air trapped at the top of the heat-exchanger casting (needs purging)
- Low system water flow - failed or air-bound circulator
- Closed zone/isolation valves restricting flow
- Faulty or open casting temperature switch
- System low on water / low pressure
What you can safely check
- Check the system pressure gauge reads roughly 12-15 psi when cool; top up via the fill valve if low and you know how
- Confirm the circulator pump is running (you can feel it humming)
Beyond these checks, do not open the unit or touch gas/electrical parts — BC law requires a licensed gas fitter. Call us for a proper diagnosis.
Error E12 usually leaves you without heat or hot water and can indicate a safety-related fault. Don't keep resetting it — call for priority after-hours Dunkirk repair.
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Parts often behind Dunkirk error E12
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Dunkirk Error E12 Repair Across Metro Vancouver
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