Error E.04 – .00

Safety precautions:

- If you smell gas or suspect a leak: stop using appliances, do not use electrical switches or phones inside the property, ventilate by opening doors/windows if safe, evacuate everyone, and call the national gas emergency number immediately. Do not attempt internal repairs.

- If you will remove the boiler cover for visual checks, isolate electrical power at the consumer unit first. If you are not comfortable doing this, wait for an engineer.

- Do not attempt to remove or repair the gas valve or any gas-carrying components unless you are Gas Safe registered — this is dangerous and illegal for unqualified persons.

Initial homeowner checks you can safely do:

1. Record the exact error code and when it appeared. Try a single reset: press and hold the reset button for 3–5 seconds and observe if the boiler attempts to restart. If the code clears and the boiler runs normally, monitor closely. If it returns, do not keep resetting.

2. Confirm gas supply: check other gas appliances (hob, fire) work, ensure the gas meter/service cock is open and prepay meters have credit. If the gas supply is off, restoring it may clear the fault.

3. Confirm electrical supply: check the boiler display is powered and check household fuses/RCDs. A loss of supply or mains spikes can cause communication faults.

4. Check system pressure: ensure the central heating pressure is within the normal range (typically ~1–1.5 bar). Extremely low pressure can cause unrelated faults; top up only if you know how and follow the boiler manual.

5. Visual inspection (only if you are comfortable and power is isolated): look for obvious signs of damage, water ingress, burnt connectors or loose plugs around the gas valve and wiring loom. Do not touch internal components with power connected. Re-seating a visibly loose connector (with power off) may resolve a poor connection, but do not attempt internal repairs.

6. Photograph the error display and any wiring/connector issues to show an engineer — this speeds diagnosis.

Specific diagnostic and repair steps (for a qualified Gas Safe engineer):

- Verify the fault with an appropriate service tool or meter and follow Baxi service procedures. Check for temporary lockouts versus permanent communication faults.

- Inspect the gas valve connector and wiring harness for continuity, corrosion, water damage, or signs of overheating. Re-seat or replace damaged plugs/wiring as required.

- Measure command voltage from the PCB to the gas valve during an ignition attempt (typically 24 V AC on many systems) and measure coil resistance on the gas valve to the manufacturer's specification.

- Check related fuses, PCB connectors and the board itself for damage. Replace PCB only after confirming the gas valve and wiring are OK.

- Inspect the air/gas unit assembly (including fan and associated sensors) because failures elsewhere can present as gas valve or comms faults. Replace the faulty component (gas valve/air-gas unit/PCB) per Baxi guidance.

- After repair, perform a full gas tightness test and safe combustion check, then run the boiler through several cycles to confirm the fault is cleared.

Final notes:

- Because this is a safety-critical gas control fault, if the simple homeowner checks above do not clear the error, contact a Gas Safe registered engineer. Do not continue to reset the boiler repeatedly — repeated lockouts indicate a persistent fault and unsafe conditions.

- If you smell gas at any time, follow the gas emergency steps in the safety section and contact the emergency gas service immediately.