Saunier Duval F.63 Fault Code: Causes, Fixes & Repair Costs
What does the Saunier Duval F.63 fault code mean?
The F.63 fault code points to an electronic failure within the boiler's main printed circuit board (PCB), specifically involving the EEPROM — a small memory chip that stores the board's operating data. When this chip malfunctions or loses communication with other electronic components, the boiler detects an internal data or signalling error and shuts down as a precaution. Because the PCB is responsible for coordinating every major component — the pump, gas valve, sensors, and ignition — even a partial failure here can bring the whole boiler to a standstill. Saunier Duval is part of the Vaillant Group and shares its electronics platform with Vaillant and Glow-worm boilers, so F.63 carries the same meaning across all three brands. It is also worth noting that F.61, F.62, F.63, and F.64 codes can sometimes appear interchangeably on the same boiler; they often share a root cause, so diagnosing one thoroughly can resolve others.
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 failing PCB (including EEPROM chip) Common
The most frequent culprit. The PCB's EEPROM memory chip can degrade over time, particularly in older boilers, leading to data corruption or communication loss between the board and the components it controls. A failed PCB will usually require a full board replacement rather than a component-level repair.
- Defective gas valve Common
If the PCB itself checks out correctly, the gas valve is the next component under suspicion. An engineer will test the electrical resistance across the valve's coils; a reading outside the specified tolerance indicates the valve is faulty and needs replacing. In some cases both the gas valve and PCB are defective simultaneously.
- Loose or corroded wiring connections Sometimes
Poor electrical connections between the PCB and downstream components — the gas valve, pump, or sensors — can disrupt the signals the board relies on and trigger an F.63. Vibration over years of operation can work terminals loose, and damp environments can cause corrosion at connector blocks.
- Moisture ingress affecting electronics Sometimes
Water finding its way onto the PCB or its connectors — whether from a nearby leak, condensation, or a poorly sealed casing — can cause short circuits and erratic EEPROM behaviour. This is particularly associated with pre-2011 models whose enclosures were less well protected.
- Incorrect PCB configuration after installation or servicing Sometimes
When a new PCB or boiler has been installed, the replacement board sometimes needs to be configured or coded to match the specific appliance. If this step was skipped or done incorrectly by the previous engineer, the EEPROM may hold mismatched data and trigger F.63.
- Intermittent overload at peak demand Rare
Some owners report F.63 appearing specifically when hot water demand is at its highest — for example, during a shower. Running at or near maximum capacity can expose a marginal electronic component that otherwise holds together at lower loads.
How to fix it
- Stop resetting the boiler repeatedly DIY safe
A single reset is reasonable to attempt, but pressing the reset button again and again after an F.63 is not recommended. Repeated resets can mask the underlying fault, stress other components, and in some circumstances create safety risks. If the fault returns after one reset, leave the boiler off and move to the next step.
- Check that your gas supply is working DIY safe
Before calling an engineer, confirm that other gas appliances in your home — a gas hob, for example — are working normally. If nothing gas-powered is functioning, the issue may be with your gas supply rather than the boiler. Contact your gas supplier if you suspect a supply interruption.
- Arrange a visit from a Gas Safe registered engineer for diagnosis Gas Safe engineer
Because F.63 is rooted in the boiler's electronics and gas valve circuit, all further investigation must be carried out by a qualified Gas Safe engineer. They will use a multimeter to check resistance values across the gas valve coils, inspect PCB connections, and assess whether the EEPROM fault is isolated to the board or linked to a downstream component.
- Engineer to test the gas valve resistance Gas Safe engineer
The engineer will measure the resistance across the gas valve's coils and compare the reading against the manufacturer's specification. A reading outside tolerance confirms the valve is faulty. If the valve tests correctly, attention turns to the PCB itself.
- Engineer to inspect all wiring and connector blocks Gas Safe engineer
The engineer should check every connector leading to and from the PCB — particularly those serving the gas valve, pump, and temperature sensors — using a multimeter to identify any open circuits, high-resistance joints, or signs of corrosion. Re-seating loose connectors sometimes resolves F.63 without the need for a part replacement.
- Replace the faulty component (PCB or gas valve) Gas Safe engineer
Once the diagnosis is clear, the engineer will replace the defective part. If a new PCB is fitted, it will need to be correctly configured for your specific boiler model before the appliance is restarted — skipping this step can cause the fault to reappear immediately. If both the gas valve and PCB are suspect, the engineer may recommend replacing both to avoid a repeat call-out.
- Consider whether repair or boiler replacement makes better financial sense DIY safe
If your Saunier Duval boiler is 12 years old or more, or if the engineer identifies that several components are worn alongside the PCB, it may be worth getting a new boiler quote alongside the repair quote. PCB replacement is one of the more expensive single repairs on a boiler, so putting that money towards a new, efficient appliance can be the better long-term decision.
Parts you may need
- Printed Circuit Board (PCB) · from £220
- Gas valve · from £120
- Wiring loom / connector harness · from £35
- NTC flow or return thermistor · from £18
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 £250–£500, depending on the underlying cause.
Frequently asked questions
Is F.63 on a Saunier Duval always a PCB fault?
Not always, although the PCB is the most common cause. The F.63 code flags an EEPROM or electronic communication error, which usually originates on the main board — but a faulty gas valve, corroded wiring, or a misconfigured replacement PCB can produce exactly the same code. A Gas Safe engineer needs to work through the diagnosis systematically rather than automatically ordering a new PCB. In some cases a loose connector is the only issue and the repair cost is minimal.
Can F.63 appear alongside F.61, F.62, or F.64 on the same boiler?
Yes. On Saunier Duval (and the related Vaillant and Glow-worm ranges) these codes sit in the same electronic fault family. A single underlying problem — such as a deteriorating PCB or a failing gas valve — can cause the boiler to cycle through different codes on different occasions. If you have seen more than one of these codes on your boiler, tell the engineer when you call; it helps them build a clearer picture before they arrive.
How much does it cost to fix an F.63 fault in the UK?
Most homeowners pay somewhere between £250 and £500 all-in, depending on which component needs replacing. A gas valve swap typically costs around £200–£320 including parts and labour, while a PCB replacement tends to sit in the £320–£450 range. In straightforward cases where only a wiring connector needs re-seating the bill will be considerably lower — largely a call-out and labour charge. If the engineer finds that both the PCB and gas valve need replacing, costs can push above £600, at which point a new boiler quote is worth having for comparison.
Is it safe to keep using the boiler while it shows F.63?
No. F.63 is a lockout fault, which means the boiler has already shut itself down as a safety measure. You should not attempt to keep forcing it back on with repeated resets. Leave the boiler off, ensure your home stays warm through other means if needed, and contact a Gas Safe registered engineer promptly. Repeatedly overriding a lockout can put additional strain on components and, depending on the root cause, could create a safety risk.