Overview
On a Baxi Avanta boiler the E4 code commonly means the boiler has failed to establish or maintain ignition or there is poor circulation preventing normal firing. Different Baxi documents list E4 for poor circulation on Avanta models and other Baxi materials associate similar numeric codes with ignition/flame problems, so the practical effect you will see is the boiler attempting to start but locking out or repeating start attempts with no flame. This error can be caused by simple, temporary issues — air trapped in the system, low system pressure, a frozen condensate pipe or an interrupted gas supply — or by more serious faults such as a failed ignition electrode, gas valve fault, pump failure or PCB/sensor issues. Severity ranges from low (easy homeowner fixes) to high (gas/ignition faults that are safety-critical). You can safely try a few basic checks and resets yourself, but if there is any smell of gas, repeated lockouts, persistent E4 after basic checks, or you are uncomfortable performing the steps, stop and get a Gas Safe registered engineer to diagnose and repair the boiler.
Possible Cause: Ignition failure
Troubleshooting Steps
Safety first:
- If you smell gas or suspect a gas leak: do not operate the boiler, do not switch electrical items on or off, open doors/windows, leave the property immediately and call the national gas emergency number (or your local gas emergency service) from a safe location.
- If you suspect carbon monoxide (nausea, headaches, soot, yellow pilot light), turn the boiler off, ventilate the area, evacuate and call a Gas Safe engineer immediately.
- If you are unsure, stop and call a qualified engineer. Never attempt internal gas or electrical repairs yourself.
Initial homeowner checks (safe, low-skill steps):
1. Check the display and note any lockout indications or flashing lights. Look in the manual for reset procedure for your exact Avanta control layout.
2. Check system water pressure on the boiler gauge. Aim for roughly 1.0–1.5 bar when the system is cold. If pressure is low (below ~1.0 bar), the boiler may refuse to ignite. If low, repressurise via the filling loop following the boiler manual instructions, then re-check for leaks.
3. Bleed radiators to remove trapped air: turn the heating off and allow it to cool, open radiator bleed valves one at a time with a bleed key until water (no air) flows, then re-check system pressure and top up if it has dropped.
4. Check the gas supply: ensure other gas appliances (hob, cooker) are working. If you have a prepayment meter, make sure it has credit and the meter is switched on. Confirm the gas isolation valve at the meter or appliance is open.
5. Check external condensate and flue terminals: in freezing weather a condensate pipe can freeze — thaw with warm (not boiling) water. Ensure the flue terminal is not blocked by debris, birds' nests, or snow.
Reset and observation:
6. Reset the boiler once you have completed the checks above. Use the reset button or selector as described in the Avanta manual (hold reset for 5–10 seconds). Allow the boiler to attempt a restart and observe behaviour and any fault lights/codes.
7. If the boiler fires and the fault clears, run the heating/hot water to ensure normal operation and re-check pressure later for any unexplained drops (which indicate a leak or other issue).
When to call a professional (Gas Safe engineer):
- The E4 code returns after the above checks and a single reset, or the boiler locks out repeatedly.
- You detect a gas smell or suspect a gas leak, carbon monoxide, or a hazardous situation.
- System pressure repeatedly falls or cannot be maintained after topping up (possible leak or defective expansion vessel/valve).
- You hear unusual noises (pump seizure, banging) or suspect pump/valve/fan/electrode/PCB faults.
What a Gas Safe engineer will check and why you should call one:
- Confirm gas supply pressure and gas valve operation, test ignition electrode/ignition lead and flame detection (ionisation) components, inspect the PCB and sensors for faults, check the pump and system circulation for blockages or seized components, and examine flue/condensate arrangements. These involve live gas and electrical work and need qualified diagnosis and safe repair.
Notes and prevention:
- Do not keep repeatedly resetting the boiler; repeated lockouts can mask a serious fault and risk further damage.
- Keep the boiler serviced annually by a Gas Safe registered engineer to reduce ignition and circulation faults.
- When you call an engineer, be ready to give the exact fault code, the boiler pressure reading, when the fault occurs, and any recent changes (service, new radiator work, freezing weather) to speed up diagnosis.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Avanta Range.