Protherm F.67 Fault Code: Causes, Fixes & Repair Costs
What does the Protherm F.67 fault code mean?
The F.67 code appears when the boiler's control electronics receive a flame signal that is absent, unreadable, or doesn't make sense — often described internally as an implausible or irregular ionisation signal from the ASIC (Application-Specific Integrated Circuit) chip on the main board. In plain terms, the boiler cannot confirm whether a flame is present or not, so it shuts down as a safety precaution. This fault sits at the intersection of the flame-detection system and the main PCB, meaning the root cause could be a dirty or faulty ionisation electrode, damaged wiring, or a failing control board. Because the boiler has locked out to protect itself and the property, the fault will need to be properly diagnosed before the appliance can run reliably again.
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
- Dirty or worn ionisation (flame-sensing) electrode Common
The ionisation electrode sits inside the burner flame and detects it by measuring a tiny electrical current passing through the flame. Over time, carbon deposits build up on the electrode tip, weakening the signal until the PCB can no longer confirm ignition reliably. This is the most frequent trigger for F.67 and is typically identified during an annual service. Electrodes generally last three to five years depending on how hard the boiler works.
- Damaged or degraded electrode wiring and leads Sometimes
The lead connecting the ionisation electrode to the PCB can suffer from heat exposure, chafing, or moisture ingress over time. A break or high-resistance fault in this wiring produces an unreliable or absent signal at the board — the same symptom as a faulty electrode itself. An engineer will test continuity and insulation resistance along the entire ignition and sensing circuit to rule this out.
- Moisture or internal water leak damaging electronics Sometimes
Condensation, a pinhole leak on the heat exchanger, or a poorly sealed component can allow moisture inside the boiler casing. Water and electronics are a damaging combination — even a small amount of moisture on the PCB or at connector pins can corrupt the flame signal the board receives, triggering F.67. If corrosion or water tracks are visible on the board, a simple reset will not resolve the underlying problem.
- Failed or defective PCB (main control board) Rare
The PCB interprets the signal from the ionisation electrode and makes decisions about whether combustion is safe to continue. If the board itself develops a fault — whether through component failure, age-related degradation, or moisture damage — it may misread or entirely lose the flame signal even when the electrode is working correctly. PCB failure is less common than electrode issues but is a known cause of F.67 on Protherm appliances.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on the boiler's control panel — on most Protherm models this is a dedicated button, sometimes combined with another function. Press and hold it for the duration specified in your user manual (typically three to five seconds). Allow the boiler to complete its ignition sequence. If F.67 returns immediately or after a short time, do not keep resetting — repeated resets will not fix the underlying fault and can add stress to electrical components. Move on to calling an engineer.
- Check that the gas supply to the property is working DIY safe
Before calling an engineer, confirm that other gas appliances in the home — a gas hob, for instance — are working normally. If they are not, the issue may be with your gas supply rather than the boiler. Check whether a gas emergency control valve has been accidentally turned off, and contact your gas supplier if there is a wider supply problem.
- Have a Gas Safe engineer inspect and clean or replace the ionisation electrode Gas Safe engineer
An engineer will isolate the boiler from the gas and electricity supply, remove the casing, and access the burner assembly. The ionisation electrode tip is cleaned using fine emery cloth or replaced if it is cracked, corroded, or physically worn. This is a straightforward job often carried out as part of an annual service visit and is usually the first thing an experienced engineer will check when faced with F.67.
- Have an engineer test the electrode wiring and connector leads Gas Safe engineer
With the casing open, the engineer will check the lead running from the ionisation electrode back to the PCB for signs of heat damage, chafing, or moisture. They will test continuity and insulation resistance. A faulty lead is inexpensive to replace and should be checked before any conclusions are drawn about the PCB.
- Have an engineer inspect for internal moisture or water leak Gas Safe engineer
If wiring and the electrode are both serviceable, the engineer will look for evidence of moisture ingress — water staining, corrosion on connector pins, or damp around the heat exchanger or seals. Any active leak must be repaired before electronics are replaced, otherwise a new PCB will suffer the same fate.
- Have the PCB diagnosed and replaced if necessary Gas Safe engineer
If all other components test correctly, the engineer will diagnose the PCB as the fault source. Protherm PCBs are model-specific and often need to be ordered directly from the manufacturer or a specialist supplier. Replacement takes one to three hours. After fitting, the engineer will verify correct boiler-type settings in the control unit (an incorrect configuration can itself produce implausible flame signals) and carry out a full ignition test.
- Call a Gas Safe registered engineer if F.67 persists after a single reset Gas Safe engineer
This fault code consistently points to components — the ionisation electrode, its wiring, or the PCB — that must be worked on by a Gas Safe registered engineer. You can verify any engineer's registration at gassaferegister.co.uk before they begin work. Attempting to access or adjust gas or electrical components yourself is unsafe and illegal without the appropriate qualifications.
Parts you may need
- Ionisation / flame-sensing electrode · from £25
- Electrode connecting lead / ignition lead · from £20
- PCB (main control board) — Protherm specific · from £280
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 £90–£380, depending on the underlying cause.
Frequently asked questions
Can I fix Protherm F.67 myself by resetting the boiler?
You can try a single reset — that is the one homeowner step worth attempting. If the fault clears and does not return, the boiler may have experienced a temporary signal glitch. However, if F.67 comes back straight away or reappears within a short time, repeated resetting will not help and may put additional stress on the electronics. At that point the fault needs a Gas Safe registered engineer to diagnose and repair the underlying cause, whether that is a dirty electrode, damaged wiring, or a failing PCB.
How much does it cost to fix Protherm F.67 in the UK?
If the ionisation electrode simply needs cleaning, the cost is typically absorbed into a service visit (around £80–£120). Replacing the electrode itself adds roughly £25 for the part, keeping the total bill modest. If the PCB turns out to be at fault, expect to pay significantly more — PCB replacement on a Protherm boiler typically costs between £350 and £700 once parts and labour are included, as the board is a complex, model-specific component. The headline repair range of £90–£380 covers the majority of F.67 faults; PCB replacement sits above that and may prompt a conversation about whether replacing an older boiler makes more financial sense.
How do I know if it is the electrode or the PCB causing F.67?
You cannot tell from the fault code alone — both a dirty electrode and a failed PCB produce the same F.67 display. A Gas Safe engineer will start with the simpler and cheaper components: cleaning or replacing the ionisation electrode and testing its wiring. Only if those checks come back clear will they conclude the PCB is at fault. This logical approach means most F.67 repairs end up being electrode or wiring jobs rather than PCB replacements.
Is it worth repairing a Protherm boiler showing F.67, or should I replace it?
For a boiler under ten years old in otherwise good condition, repairing an electrode or wiring issue is almost always worthwhile. Even a PCB replacement can make sense if the boiler is relatively young. For a boiler over ten to twelve years old, the general guidance is to weigh the repair cost against the price of a new boiler — if the repair comes to more than half the cost of a replacement, a new, more efficient boiler is often the better long-term investment, particularly given rising energy costs.