Overview
H.03 – .02 on a Baxi 200 / 400 Combi means the boiler has detected a flame error: the burner is not producing or the boiler is not detecting a flame (no ionisation current) during operation. In practice the boiler has tried to ignite or maintain flame and then shut down as a safety measure because the flame detector did not sense a stable combustion flame. Common causes are interruption or absence of gas supply, low gas pressure, a faulty ignition electrode or flame sensor (ionisation probe), a failing gas valve or problems with the air/gas assembly, or flue/ventilation problems that affect combustion. This is a safety-critical fault. The lockout is deliberate to prevent unsafe operation. Some causes are simple and can be checked and cleared by a homeowner (for example checking the gas supply, resetting once, clearing a frozen condensate pipe or an obvious flue blockage), but most root causes (ignition electrode, gas valve, wiring, PCB or combustion adjustments) require a Gas Safe registered engineer. If the code clears after a single reset it may have been a temporary glitch; repeated or persistent H.03-.02 faults always need professional investigation.
Possible Cause: Flame error – no flame during operation.
Troubleshooting Steps
Safety precautions:
1) If you smell gas, do not try to operate the boiler. Turn off the gas supply at the meter or gas isolation valve if safe to do so, ventilate the area, do not use electrical switches or naked flames, evacuate the property if the smell is strong and call the gas emergency number or your supplier immediately. 2) Do not open the boiler casing or attempt internal electrical or gas repairs unless you are a Gas Safe registered engineer.
Initial checks you can safely do yourself:
1) Check other gas appliances (hob, gas fire) to confirm the property has a gas supply and that any prepayment meter has credit. 2) Check the boiler has power (display lit) and the fuse/circuit breaker hasn’t tripped. 3) Check system water pressure on the boiler gauge; if it is below 0.5 bar the boiler may not attempt ignition — top up to the normal operating pressure (typically 1–1.5 bar) if you know how and it is safe to do so. 4) Try a single boiler reset using the reset button (hold for the time specified in your manual). Only attempt one reset; if the fault returns, stop resetting. 5) Inspect the external flue terminal and air vents for obvious blockages (bird nests, leaves, snow) and clear if safe to reach. 6) In cold weather check the condensate pipe (usually a small plastic pipe exiting the property) — if frozen it can block and cause lockouts; thawing with warm (not boiling) water can sometimes clear it.
Specific diagnostic and next steps (what an engineer will check and what you should report to them):
1) If the boiler remained without flame after reset, note how often and when the fault occurred and whether it happens on heating, hot water or both. 2) If gas supply to the property is confirmed but the boiler still shows H.03-.02, do not attempt internal checks. A Gas Safe engineer will test for correct gas pressure to the appliance, check the integrity and operation of the gas valve and air/gas unit, test ignition electrodes and the ionisation/flame detection circuit, inspect wiring and connections to the PCB and safety interlocks, and check flue performance and combustion safety. 3) The engineer may also check for PCB/communication faults and run combustion tests; they will repair or replace defective components as required.
When to call a professional and what to tell them:
1) Call a Gas Safe registered engineer if the code persists after the basic checks, if you cannot confirm gas supply, if the fault recurs, or if there is any sign of gas smell or carbon monoxide risk (unusual smells, soot, pilot light issues). 2) When you call, tell them the boiler model (Baxi 200 / 400 Combi), the exact error code H.03 – .02, what you have already checked (gas supply, other appliances, pressure, reset, flue/condensate), and whether the fault is intermittent or persistent.
Final notes:
- Do not repeatedly reset the boiler; repeated lockouts point to a persistent safety issue and can cause further damage. - Any internal work on gas trains, valves, ignition electrodes, or PCB should only be done by a Gas Safe engineer. - If you ever suspect a gas leak or carbon monoxide, act immediately: evacuate, ventilate, and contact the gas emergency services and a Gas Safe engineer.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 200 / 400 Combi Gas Boiler.