Dunkirk Error A21: Flame detected before gas valve opens
Lockout Alarm: during the ignition sequence the control detected a flame signal before the gas valve was opened (false/early flame). This is a safety lockout. Display shows 'A21'. Manual RESET required; refer to the troubleshooting guide. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
Lockout Alarm: during the ignition sequence the control detected a flame signal before the gas valve was opened (false/early flame). This is a safety lockout. Display shows 'A21'. Manual RESET required; refer to the troubleshooting guide.
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 A21
- Contaminated, shorted or misaligned flame sensor giving a false flame signal
- Gas valve leaking through / not sealing
- Moisture or carbon on the flame rod
- Control module fault
What you can safely check
- Do not repeatedly reset - a false flame or leaking gas valve is a safety concern
- If you smell gas, shut off the gas and call your utility
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 A21 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 A21
Genuine Dunkirk parts we supply and professionally install — never for DIY.
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Dunkirk Error A21 Repair Across Metro Vancouver
Frequently Asked Questions
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