Vaillant Boiler Fault Codes Guide

We'll help you identify the fault.

Vaillant boilers are built to be reliable and efficient, but like any heating system, they can occasionally display a fault code to flag a problem. These codes are the boiler's way of letting you know something isn't working correctly — from low pressure to ignition faults or sensor issues.

This guide covers the most common Vaillant fault codes, explains what causes them, what you can safely check yourself, and when it's time to call in a professional, so you can diagnose problems quickly and keep your heating running smoothly.

Ignition & Flame Vaillant Boiler Fault Codes

F27 – Flame detected when it shouldn't be

F28 – No flame detected during ignition

F29 – Ignition failed after flame loss

F67 – Flame signal fault

F32 – Fan fault

F35 – Blocked air or flue duct

F77 – Flue non-return flap or condensate pump fault

F22 – Low water pressure

F74 – Water pressure too high

F75 – No pressure change detected on pump start

F13 – Cylinder or warm start sensor fault

F23 – Flow and return temperature spread too great

F71 – Flow or return temperature sensor problem

F49 – eBUS undervoltage or short circuit

F61 – Gas valve control fault

F63 – PCB communication fault

F65 – Main PCB overheating

F24 – Water circulation fault

F89 – Pump fault

F20 – Safety cut-out from excess temperature

F25 – Flue gas temperature too high

F76 – Primary heat exchanger overheating

F54 – Insufficient gas supply

F56 – Combustion safety lockout

F62 – Gas valve switch-off delay

F87 – Electrode malfunction

F88 – Gas valve disconnected

DIY Troubleshooting & When to Call a Professional

While some minor Vaillant boiler fault codes can be resolved safely at home, many faults require a qualified Gas Safe registered engineer. Knowing what you can handle and when to call a professional will keep your boiler safe and prevent further damage.

Safe DIY Checklist

You can attempt these actions for minor faults:

Check boiler pressure – ensure it is between 1–1.5 bar.
Reset the boiler – press the reset button once.
Check radiator valves – make sure they are open for proper circulation.
Inspect external flue – look for obvious blockages outside your home.
Check gas supply – ensure other gas appliances are working.

Do Not Attempt

Never attempt the following as they are dangerous and illegal in the UK:

Opening the boiler casing
Electrical repairs or internal wiring work
Gas repairs, adjustments, or replacements
Replacing internal sensors or components

When to contact a Vaillant boiler professional

When to Call a Professional

You should contact a Gas Safe registered engineer if:

Fault codes indicate ignition, flame, fan, or overheat issues (e.g., F27, F28, F32, F20)
The boiler repeatedly locks out or displays persistent faults
You smell gas or suspect combustion issues
You are unsure about any fault code or repair

Legal Note: Gas appliances must be serviced by a Gas Safe registered engineer in the UK. Attempting unsafe repairs can be dangerous and may invalidate your warranty or insurance.

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Areas We Cover for Vaillant Boiler Fault Codes

Experts Across Edinburgh and Surrounding Areas

Our qualified heating engineers provide reliable boiler fault fixes in Edinburgh, helping homeowners and landlords enjoy efficient, long-lasting heating systems. We cover the entire city and nearby areas, including Trinity, Wardie, Newhaven, Granton, Inverleith, Stockbridge, Craigleith, New Town, West End, Fountainbridge, Morningside, Bruntsfield, Marchmont, Newington, Craiglockhart, Corstorphine, Murrayfield, Ravelston, Leith, Restalrig, Duddingston, Portobello, Musselburgh, Davidson Mains, Silverknowes, Cramond, Cammo, and Barnton.

Whether you live in central Edinburgh or the surrounding suburbs, our team is on hand to deliver fast, professional Vaillant boiler fault fixes. We're here to help.

Vaillant Boiler Fault Codes