Heatline F67 Fault Code: Causes, Fixes & Repair Costs
What does the Heatline F67 fault code mean?
The F67 code on a Heatline boiler indicates that the boiler's control board has detected an abnormal or absent flame signal during the ignition sequence. Heatline is part of the Vaillant Group and shares the same underlying technology platform, so F67 carries identical meaning across both brands. The flame monitoring circuit expects a clean electrical signal — typically either 0V or 5V — to confirm whether a flame is present or absent. When the signal falls somewhere unexpected between those two values, or is missing entirely, the boiler cannot verify safe ignition and shuts down as a precaution. The result is a complete loss of heating and hot water until the underlying cause is identified and resolved.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or degraded flame sensor (ionisation probe) Common
The ionisation probe is the component that directly measures whether a flame is burning. Over time, the probe tip can become coated in residue or physically degrade, causing it to send an unreliable signal to the control board. This is the single most frequent trigger for F67 on Heatline boilers.
- Damaged or loose wiring to the flame sensor or ignition system Common
The wiring harness connecting the flame sensor and ignition electrodes to the PCB can develop loose connectors, chafing, or corrosion — particularly if the boiler has had recent work. A poor connection disrupts the signal pathway and can produce exactly the out-of-range voltage reading that triggers F67.
- PCB (printed circuit board) fault Sometimes
If the control board itself has been damaged — most commonly by a power surge, voltage spike, or moisture ingress — it may misinterpret or fail to process the flame signal correctly even when the sensor is functioning normally. PCB faults often appear alongside other unexplained electrical symptoms.
- Ignition module or electrode fault Sometimes
A worn or cracked ignition electrode may fail to generate a reliable spark, meaning the burner doesn't light consistently. If the flame doesn't establish properly, the sensor has nothing to detect and the F67 code follows.
- Gas valve issue Rare
If the gas valve is not opening correctly or is delivering insufficient gas pressure, the burner flame may be weak or intermittent. The ionisation probe then receives an erratic signal, which can appear as an F67 fault even though the sensor itself is healthy.
How to fix it
- Reset the boiler once or twice DIY safe
Press and hold the reset button (typically marked with a flame or reset symbol on the front panel) for around 3 seconds. Wait a few minutes to allow the boiler to attempt a restart. If F67 clears and the boiler runs normally, monitor it closely — if the fault returns within a short period, a reset alone will not fix the underlying problem and an engineer is needed.
- Check your gas supply is working DIY safe
Confirm that other gas appliances in your home (hob, oven, gas fire) are working normally. If none of them function, contact your gas supplier as there may be a supply interruption. If only the boiler is affected, the gas supply to the boiler is likely fine.
- Check boiler system pressure DIY safe
Look at the pressure gauge on the boiler front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it has dropped below 1 bar, top it up via the filling loop following your boiler's user manual. Low pressure alone won't cause F67, but it is good to rule out as part of a general check.
- Do not attempt to inspect or replace internal electrical components Gas Safe engineer
Accessing the flame sensor, ignition electrodes, wiring harness, gas valve, or PCB requires removing the boiler casing and working near the gas circuit. This work must only be carried out by a Gas Safe registered engineer. Attempting it yourself risks injury, gas leaks, and will void any remaining warranty.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
An engineer will remove the casing, inspect the ionisation probe and electrode for wear or contamination, check all wiring connections for corrosion or damage, and test the PCB for correct signal processing. They will replace whichever component is at fault — most commonly the flame sensor, ignition electrode, or wiring — and carry out a full function test before signing off the repair.
Parts you may need
- Ionisation probe (flame sensor) · from £25
- Ignition electrode · from £20
- Ignition lead / HT lead · from £15
- Gas valve · from £120
- PCB (control board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£350, depending on the underlying cause.
Frequently asked questions
Is the Heatline F67 fault dangerous?
F67 is not typically an immediate safety emergency — the boiler has shut itself down as a precaution, which is exactly what it should do. However, you should not keep attempting to reset the boiler repeatedly without investigating the cause, and the fault should be looked at by a Gas Safe registered engineer promptly rather than left indefinitely.
Can I fix the F67 fault myself?
The only homeowner-safe steps are resetting the boiler (up to two or three times) and checking that your gas supply is on. All internal components — the flame sensor, electrodes, wiring, gas valve, and PCB — must be inspected and replaced by a Gas Safe registered engineer. Working inside the boiler yourself could void your warranty and create a safety hazard.
Why does F67 keep coming back after a reset?
A reset clears the fault flag on the control board but does not fix the component causing the problem. If the ionisation probe is worn, a connector is loose, or the PCB is damaged, the same abnormal flame signal will reappear as soon as the boiler tries to ignite again. Repeated resets without a repair can also cause additional wear, so it is best to limit resets to two or three attempts and then call an engineer.
How much does it cost to fix an F67 fault on a Heatline boiler?
Most homeowners pay somewhere between £120 and £350, depending on what needs replacing. A straightforward flame sensor or ignition electrode swap, including labour, typically falls in the lower part of that range. If the PCB turns out to be damaged — for example after a power surge — costs can rise above this, as the board itself can cost £150–£200 in parts alone before labour is added. An engineer should be able to give you a firm quote once they have diagnosed the specific cause.