Overview
Error E.04 – .10 on a Baxi 200/400 combi indicates a failure to ignite the burner — the boiler attempted to light but did not detect a sustained flame. Common causes are no gas supply (meter off, empty prepay credit, upstream isolation valve closed), a blocked/ frozen condensate or flue/air inlet preventing safe ignition, or an internal ignition/combustion fault (ignition electrode/spark, flame detection/ionisation circuit, gas valve, fan or PCB). The boiler will usually go to lockout to protect the system and stop repeated unsafe ignition attempts. Severity: this fault prevents the boiler supplying heating and hot water and can be serious if you smell gas. If you detect a gas smell, treat it as an emergency — evacuate the property and contact the gas emergency number immediately. If there is no smell of gas, the issue is often less immediately dangerous but still requires prompt attention because it leaves you without heat/hot water and may indicate a faulty gas control or ignition system. Basic external checks can be done by a homeowner, but any work on gas components, internal electrics, or replacing ignition parts must be carried out by a Gas Safe registered engineer (or your local qualified service).
Possible Cause: Failure to light (could be gas supply issue).
Troubleshooting Steps
Safety first:
- If you smell gas: leave the building immediately, do not operate switches, phones or open flames; call your gas emergency number from a safe location. Do not attempt any checks.
- If you do not smell gas, isolate electrical power to the boiler before removing covers for any inspection. Do not open or attempt repairs to gas-carrying components or the combustion chamber unless you are Gas Safe qualified.
- Do not keep repeatedly resetting the boiler — repeated reset attempts can hide a developing fault and may be unsafe.
Initial homeowner checks (safe, non-invasive):
1) Note the exact fault code and any other displayed codes or LEDs. Try a single reset: press and release the reset button (hold 5–10 seconds if applicable) and observe. If it restarts and runs normally for a while the fault may have been transient. If the same E.04 – .10 returns, proceed with the checks below.
2) Check gas supply: confirm other gas appliances (cookers, gas fire) will light or are working. If you have a prepayment meter check credit. Check the gas meter isolation lever and any external isolation valves are open. If no other appliances work, contact your gas supplier.
3) Check boiler isolation and power: ensure the boiler is switched on at the mains, timers/thermostats are calling for heat, and the boiler's fused spur or RCD hasn’t tripped. Verify the boiler pressure gauge is in the normal range (typically around 1–2 bar). Low water pressure does not directly cause ignition failure but will stop the boiler from operating.
4) Check condensate/drain and flue/air inlet: in cold weather a condensate pipe may be frozen or blocked — locate the external condensate discharge (usually a small plastic pipe) and carefully thaw with warm (not boiling) water. Check the external flue terminal and air inlet for obvious obstruction (birds nest, bags, leaves) from outside; do not climb on roofs unless safe and competent.
What you can safely inspect (visual, non-invasive):
- Look at the boiler's exterior and flue for visible damage or blockage.
- Listen when you press for hot water or heating: do you hear the boiler trying to ignite (a clicking sound)? If you hear nothing at all, that suggests no ignition attempt which may indicate lack of gas or an electrical/PCB issue.
- Check for any visible error history or service log if your boiler display provides it.
Do not do (leave for a qualified engineer):
- Do not remove the burner or gas/air assembly, do not attempt to adjust or test the gas valve, and do not disassemble the ignition electrode or wiring unless you are Gas Safe registered. The training material shows technicians checking the electrode gap (~4 mm), spark connections and electrode seals — this is specialist, live-gas work.
If basic checks fail to restore operation, likely causes requiring a Gas Safe engineer include: persistent no gas to the burner despite supply being present (faulty internal gas valve or PCB communication), failed ignition electrode/spark lead, faulty flame detection/ionisation circuit, fan or air/gas unit faults, or internal wiring/PCB issues. A qualified engineer will run safe live tests, check ignition spark and ionisation current, inspect/replace the electrode or seal, test the gas valve and fan, check for false flame signals and examine the PCB and air/gas unit.
When to call a professional and what to tell them:
- Call a Gas Safe registered engineer if: the boiler will not light after your basic checks; you confirmed gas to the property but boiler will not ignite; the condensate or flue check didn’t help; or the boiler locks out repeatedly after resets.
- Tell the engineer the exact error code (E.04 – .10), what checks you have already completed (gas to other appliances yes/no, condensate thawed, flue visually clear, reset tried once, pressure checked), whether you smell gas, and any noises or behaviour (clicking, repeated lockouts). This speeds diagnosis.
Summary: carry out the safe, non-invasive checks above; if the boiler still fails to light call a Gas Safe engineer. Do not attempt internal boiler repairs or gas component replacement yourself.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 200 / 400 Combi Gas Boiler.