Glow-worm F63 Fault Code: Causes, Fixes & Repair Costs
What does the Glow-worm F63 fault code mean?
The F63 code on a Glow-Worm boiler indicates a fault detected within the main control board (PCB) — the central unit that coordinates signals between all the boiler's electrical components. When the PCB develops a problem, the boiler cannot operate safely, so it enters a full lockout, cutting off both heating and hot water until the issue is resolved. F63 sits within a family of related PCB fault codes (F61, F62, F64, F65, and F67) that all point to control board or associated electrical circuit problems. If you are seeing any of these codes alongside F63, the same diagnostic process applies.
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 failed PCB Common
The PCB can degrade over time through normal wear, repeated heating and cooling cycles, or moisture ingress from condensation or internal leaks. Dry solder joints on the board can cause intermittent failures that eventually become permanent. This is the most common root cause of an F63 lockout.
- Loose or damaged internal wiring Common
Vibration from the boiler's pump and fan can gradually work wiring connectors loose over months and years. Heat exposure inside the boiler casing can also damage wire insulation, creating poor or broken connections between the PCB and other components. The boiler may have worked perfectly until one connection finally gave out.
- Faulty ignition leads Sometimes
The ignition leads carry high-voltage signals to the electrodes. If a lead develops a crack, weak connection, or tracking fault, the PCB can register an electrical circuit error and trigger an F63 lockout. An engineer will typically test these with a multimeter as part of the standard diagnostic process.
- Incorrectly fitted or unconfigured replacement PCB Sometimes
If a PCB was recently replaced, the fault may arise because the wrong board variant was installed or because the new board was not correctly configured for your specific boiler model. This is a known cause of F61–F67 codes appearing on 'repaired' boilers.
- Environmental damage to electronics Rare
Prolonged exposure to high humidity or an internal water leak dripping onto the PCB can cause corrosion or short circuits on the board. Excessive heat within the boiler casing — caused by a blocked flue or inadequate ventilation — can also accelerate component failure.
How to fix it
- Reset the boiler once or twice DIY safe
On most Glow-Worm models, rotate the CH temperature knob to the reset position (marked with a power symbol), hold it for around 30 seconds, then turn it back to your desired temperature. A single successful reset may clear a transient electrical glitch. Do not reset more than two or three times — if the F63 returns promptly, a reset alone will not fix the underlying problem and you risk masking it.
- Check the boiler's power supply DIY safe
Confirm the boiler's isolator switch is on and that the circuit breaker or fuse for the boiler has not tripped at the consumer unit. A brief power interruption can sometimes cause a spurious fault code that clears once power is properly restored.
- Do not attempt any internal electrical work yourself Gas Safe engineer
Inspecting, testing, or replacing the PCB, ignition leads, or any internal wiring requires a Gas Safe registered engineer. These components carry mains voltage and are directly connected to the gas control system. DIY work on these parts is unsafe and potentially illegal.
- Book a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
An engineer will use a multimeter to systematically test each element of the electrical circuit — ignition leads, wiring loom connectors, and PCB outputs — to pinpoint the exact failure. This logical, component-by-component approach prevents unnecessary parts being replaced.
- Engineer to repair or replace the faulty component Gas Safe engineer
If a loose connector or damaged wire is found, it can often be repaired at relatively low cost. Faulty ignition leads are straightforward and inexpensive to swap. If the PCB itself has failed, the engineer will source the correct board for your specific model and configure it properly before fitting. On older boilers, the engineer may advise weighing up repair cost against boiler replacement.
Parts you may need
- Replacement PCB (control board) · from £280
- Ignition lead set · from £35
- Wiring harness / loom · from £55
- PCB configuration / programming service · from £60
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 £150–£550, depending on the underlying cause.
Frequently asked questions
Can I fix a Glow-Worm F63 fault myself?
No. The F63 code points to a fault inside the boiler's electrical circuitry or control board, and any investigation or repair work on those components must be carried out by a Gas Safe registered engineer. The only safe homeowner actions are attempting a reset (once or twice) and checking the mains power supply is intact. If those steps do not clear the code, call a professional.
How much does it cost to fix a Glow-Worm F63 fault in the UK?
For most people, the total bill including diagnosis and repair lands somewhere between £150 and £550. A straightforward wiring or ignition lead fix sits at the lower end, while a full PCB replacement (parts plus labour) typically comes to around £450–£550. The PCB part alone generally costs £180–£400 depending on the model. Note that on very old boilers an engineer may advise replacement rather than repair if other components are also showing signs of wear.
My boiler also shows F61 and F62 — are these the same fault?
Yes, the F61, F62, F63, F64, F65, and F67 codes all fall within the same PCB and electrical-circuit fault family on Glow-Worm boilers. They each indicate slightly different internal diagnostic triggers, but the root causes — PCB failure, wiring faults, ignition lead problems — and the repair approach are essentially the same. Report all the codes you have seen to your engineer, as the combination can help them narrow down the fault faster.
Is it worth repairing an F63 fault, or should I replace the boiler?
That depends on the age and overall condition of your boiler. If the boiler is under ten years old and otherwise in good condition, repairing a wiring fault or even replacing the PCB is usually worthwhile. If the boiler is older and the PCB has failed, the repair cost could exceed £500 — at which point many engineers recommend replacement, especially as a failing PCB can reveal underlying issues with other components such as the pump or fan. As a rule of thumb, if the repair quote is more than half the cost of a comparable new boiler, replacement tends to offer better long-term value.