Error E.04 – .06

Safety precautions:

- If you smell gas, evacuate the property immediately and call your gas emergency number. Do not operate electrical switches or the boiler.

- Do not open the boiler casing or attempt internal repairs unless you are a Gas Safe registered engineer. Working on gas or flue components is hazardous.

- Turn the boiler off at the programmer and isolate electrical supply at the fuse or isolation switch before doing any external checks.

Initial homeowner checks you can safely do:

1. Note when the code appeared and any recent events (power cuts, servicing, loud noises, loss of hot water). This helps the engineer.

2. Check system water pressure on the boiler gauge. Aim for approximately 1–1.5 bar for most Baxi combi boilers. If pressure is below about 0.5 bar the boiler may not circulate; top up the system using the filling loop to the recommended level and follow the boiler manual for repressurising. After topping up, try a single reset.

3. Inspect the external flue terminal (outside the property) for visible blockages: birds’ nests, debris, snow or ice build-up. Remove obvious external obstructions safely (use a ladder and stable footing) but do not force or dismantle the flue.

4. Bleed radiators to remove trapped air and restore circulation. Airlocks can prevent flow and cause overheating of parts of the boiler.

5. With the boiler powered and calling for heat (or DHW), carefully feel the boiler flow and return pipes (not the flue). If the flow pipe becomes very hot while the return stays cold, circulation may be poor. You may also be able to hear whether the pump is running (a low humming). If the pump appears silent when there is a demand, circulation is likely the problem.

Specific diagnostic steps and safe corrective actions (homeowner level):

1. Reset once: press and hold the boiler reset button for the time specified in your manual (usually a few seconds). If the error does not clear or returns immediately, do not keep resetting repeatedly.

2. If pressure was low and you have topped up, test whether the boiler runs normally after a reset. If the code returns, proceed to the next checks.

3. Check radiator and system valves are open (thermostatic valves not closed, isolation valves to the boiler open). Ensure any external pump switches (if present) are on.

4. If you suspect air in the system after bleeding radiators, re-check pressure and repressurise if it has dropped.

5. Check for visible signs of leaks around the boiler or pipework which could cause low pressure and circulation loss.

When to call a professional (must-call situations):

- The E.04 – .06 code persists after the simple checks above and a single reset.

- You detect a blocked flue you cannot safely clear, or you suspect fan/flue terminal damage.

- The pump is not running or you suspect the pump is seized, or zone valve/electrical faults.

- You’re unsure about the cause, or there are signs of internal leaks, burning smells, or blackening around the flue.

Why call a Gas Safe engineer and what they will do:

- This fault often needs electrical and gas-safe diagnostics: they will test the flue thermistor, pump operation, flow/return sensor readings, fan and gas/air unit behaviour, and PCB communications. They can safely carry out replacements (flue sensor, pump, fan, valves) and confirm flue integrity and correct combustion.

Other important notes:

- Do not attempt to replace flue sensors, fan assemblies, gas valves, or work inside the sealed boiler casing unless you are qualified and registered.

- Record the error code, date/time, and any symptoms to provide to the engineer.

- If the boiler locks out repeatedly after a reset, leave it locked and call a Gas Safe engineer. Repeated resets can be dangerous and may worsen damage.