Error E53

Safety precautions:

1. If you smell gas, feel unwell, suspect carbon monoxide, or have a CO alarm sounding, leave the property immediately and call the gas emergency number and emergency services. Do not re-enter until it is safe.

2. Before any inspection, switch the boiler off at the isolator and turn off the gas supply if you can do so safely. Allow the boiler to cool. Wear gloves and eye protection for outdoor checks.

3. Do not try to dismantle the sealed flue, remove the boiler casing, or work on gas components unless you are a qualified Gas Safe engineer.

Initial homeowner checks you can do:

1. Locate the flue terminal on the outside of the building (usually a circular or rectangular outlet). Do a visual check from ground level or a safe vantage point — do not climb unsafely.

2. Look for obvious blockages at the terminal: bird or rodent nests, leaves, moss, soot build-up, debris, ice or snow. Also check that any cowl or guard is intact and not clogged.

3. Check that gutters or nearby plant growth are not obstructing the terminal. If the terminal is on the roof or high up and not safely reachable, do not attempt to access it yourself; call a professional.

4. Ensure the area around the flue is free of insulating materials or other obstructions pressed against the terminal.

If you find and can safely remove an external blockage:

1. Wear gloves and remove loose debris from the terminal opening only. Do not use metal tools that could damage the terminal.

2. After clearing, restore power and gas and perform a controlled reset of the boiler: switch off the boiler, wait 30 seconds, switch it back on and attempt to run heating or hot water. Observe whether the E53 clears.

3. If the code clears and the boiler runs normally, monitor for recurrence. A repeat blockage indicates an ongoing issue (e.g., nesting birds) that may require a protective terminal guard or professional corrective work.

If external terminal appears clear but E53 remains, or if you see blockage inside the flue pipe, or if the boiler was showing other symptoms (yellow flame, soot, poor combustion, frequent lockouts):

1. Do NOT attempt to access or dismantle the flue or boiler. This requires a Gas Safe engineer. Internal flue cleaning, fan replacement, thermistor or thermostat replacement, and combustion checks are specialist tasks.

2. Record any other fault codes, how long the boiler was running and any unusual signs (smell, soot marks, noises). This information helps the engineer diagnose the issue faster.

3. Contact a Gas Safe registered engineer and arrange a call-out. Tell them the appliance model, the E53 code, and what visual checks you have already performed.

Additional recommendations and warnings:

1. Have a working carbon monoxide alarm fitted in the property and test it regularly. A blocked flue increases CO risk.

2. Annual boiler servicing by a Gas Safe engineer reduces the risk of flue and combustion problems and will include checks of the flue and terminal.

3. Do not attempt DIY repairs on sealed or gas-carrying parts, the fan, the heat exchanger or the PCB. These are dangerous and illegal for unregistered persons.

When to call an engineer immediately:

1. Any sign of carbon monoxide or if the CO alarm triggers.

2. If you cannot safely clear an obvious external blockage or if E53 persists after a safe external clear and reset.

3. If the flue terminal is damaged, there is soot or discoloration around the terminal, or the boiler has other fault codes alongside E53.

A qualified engineer will inspect and, if needed, clear or replace the flue terminal, test combustion and CO levels, check and replace faulty flue thermistors or fans, and carry out any repairs to restore safe operation. Do not use the boiler until a professional confirms it is safe.