Dunkirk Error b30: Temperature rise across boiler too high - soft lockout
Soft (auto-reset) lockout: the temperature rise (delta-T) across the boiler exceeded ~100F, which almost always means water flow is too low. Burner is held off for a timed wait. Display flashes '9' then 'b' with code 30. (If this repeats 20 times the control escalates to hard lockout E30.) We diagnose and repair it across Greater Vancouver — same-day and after-hours.
Soft (auto-reset) lockout: the temperature rise (delta-T) across the boiler exceeded ~100F, which almost always means water flow is too low. Burner is held off for a timed wait. Display flashes '9' then 'b' with code 30. (If this repeats 20 times the control escalates to hard lockout E30.)
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 b30
- Low water flow - failed, air-bound, or undersized circulator
- Closed or partially closed zone/isolation valves
- Air trapped in the heat exchanger or system
- Clogged system strainer / dirty system
- Failed supply or return sensor giving a false delta-T
What you can safely check
- Confirm the circulator pump is running
- Make sure all zone and isolation valves are open
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.
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Parts often behind Dunkirk error b30
Genuine Dunkirk parts we supply and professionally install — never for DIY.
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Dunkirk Error b30 Repair Across Metro Vancouver
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