Overview
E3 on a Baxi Avanta range is the boiler telling you there is a problem with the printed circuit board (PCB) or with the internal electronics/communication that the PCB manages. The PCB is the control centre that runs safety checks, switches gas and pumps on/off, reads sensors and coordinates everything. When the PCB detects an internal fault, or when communication between the PCB and other components fails, the boiler will lock out and display E3 to protect the appliance and your home. This is generally a more serious fault than a simple pressure or ignition problem. Causes include age-related component failure, cracked or cold solder joints, corrosion from water ingress, mechanical damage from vibration, or a manufacturing/assembly fault. While you can do a few basic non-intrusive checks and a single reset, most diagnostic and repair tasks (testing voltages, re-soldering or replacing the PCB, checking internal wiring) must be carried out by a qualified Gas Safe engineer. Repeatedly resetting the boiler is not recommended and may cause further damage or mask a developing fault.
Possible Cause: Printed circuit board (PCB) fault
Troubleshooting Steps
Safety first
1) If you smell gas or suspect a gas leak, evacuate the property immediately and call the emergency gas number. Do not attempt any DIY. 2) If you find water on or under the boiler, turn off the electrical supply at the isolator and the system water supply if it’s safe to do so, then call a professional. 3) If the boiler is locked out and there are no smells or leaks, you can perform safe external checks as below, but do not open the boiler casing or touch internal components unless you are a trained, qualified engineer.
Initial homeowner checks (safe, non-intrusive)
1) Note the full error display and any other codes, the time it happened and recent events (power cut, freezing temperatures, recent plumbing work, service). 2) Check the mains power switch to the boiler and the house fuse/consumer unit to ensure the boiler has power. 3) Check external controls and thermostat: make sure the room thermostat and programmer are calling for heat, and change thermostat batteries if fitted. 4) Check boiler pressure on the gauge (aim for about 1–1.5 bar). Very low pressure can cause different faults and is simple to top up following the manufacturer’s instructions. 5) Look for signs of water ingress or corrosion around the boiler casing, and for unusual noises or vibration.
Basic resets (one attempt only)
1) Try a single reset using the boiler’s reset button: press and hold for 5–10 seconds and allow the boiler to attempt a restart. 2) If that does not clear the code, switch the boiler off at the isolator, wait 30–60 seconds, then switch it back on and see if the code clears. 3) Do not attempt repeated resets more than once or twice — repeated lockouts indicate a persistent fault and can cause further damage.
What to avoid doing yourself
1) Do not open the boiler casing or touch the PCB, wiring or gas components. Live voltages and gas systems are hazardous. 2) Do not try to re-solder PCB joints or replace the PCB yourself unless you are a qualified engineer. 3) Do not continue to operate the boiler if you can see water damage or smell burning/electrical smells.
When to call a professional and what they will do
1) Call a Gas Safe registered heating engineer if the E3 persists after the safe checks and single reset, if you see water ingress, or if the fault intermittently appears. 2) The engineer will isolate power and gas, open the boiler, visually inspect the PCB for corrosion, burnt components, or cracked solder joints, and test voltages and communication lines with a multimeter. 3) They may dry or clean the board if corrosion is minor, reflow or re-solder joints where appropriate, test related components (fan, gas valve, sensors, CSU) for faults, and ultimately replace the PCB if it is faulty or unsafe. 4) If the boiler is under warranty, provide the engineer with purchase/installation details and the boiler serial number — PCB faults on newer boilers may be covered.
Final notes
1) Keep a record of the error, what you tried, and any engineer reports. 2) Avoid repeated resets — if the fault returns, do not continue to operate the boiler. 3) Only use a qualified, Gas Safe registered engineer for diagnostics and repairs to internal electronics and gas-related components.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Avanta Range.