Vaillant F.63 Fault Code: Causes, Fixes & Repair Costs
What does the Vaillant F.63 fault code mean?
The F.63 code on a Vaillant boiler signals an EEPROM error — a problem with the small but critical memory chip embedded in the boiler's main printed circuit board (PCB). The EEPROM stores essential operating data and configuration settings; when it malfunctions or its data becomes corrupted, the PCB can no longer reliably coordinate the boiler's components — such as the pump, gas valve, and sensors — and the boiler shuts down as a safety precaution. In practice, F.63 is closely related to the F.61, F.62, and F.64 fault codes: all four point to PCB or electronic communication failures, and a boiler with an underlying board fault may cycle through any of these codes at different times. If you are seeing F.63 alongside (or alternating with) any of those codes, it reinforces that a PCB-level fault is the root cause.
General guidance only — not a substitute for professional advice. 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
- EEPROM data corruption or failure Common
The EEPROM chip on the PCB can lose its stored configuration data due to age, a power surge, or component degradation. Once the data is corrupted or the chip fails entirely, the PCB cannot operate correctly and triggers F.63. This is the most direct and common cause of this specific code.
- PCB failure Common
Beyond the EEPROM chip itself, broader failure of the main control board — cracked solder joints, burnt components, or moisture ingress — can produce the same error. The PCB controls every major component in the boiler, so even a partial board failure will typically result in a lockout.
- Incorrect PCB configuration after replacement Sometimes
If a PCB has recently been replaced (or the boiler has just been installed or serviced), the new board may not have been correctly set up or coded to the specific boiler model. An improperly configured PCB will flag an EEPROM error because the expected data does not match the board's stored settings.
- Faulty wiring, connectors, or NTC thermistors Sometimes
Damaged wiring harnesses, corroded or loose connector plugs, or failing NTC thermistors on the flow and return pipes can interfere with the PCB's ability to read sensor data. In some cases this electrical noise or missing signal is interpreted as an EEPROM communication fault, leading to F.63 being displayed even though the board itself is intact.
How to fix it
- Do not repeatedly reset the boiler DIY safe
A single reset (hold the reset button for around 3 seconds, then release) is worth attempting once to see if the fault clears. However, repeatedly resetting a boiler showing F.63 is not recommended — it will not fix an electronic fault and may introduce additional issues. If the code returns immediately or within a short time, stop resetting and move on.
- Check for a recent power surge or electrical event DIY safe
Consider whether there has been a power cut, surge, or electrical work in the home recently. If so, let the boiler sit without power for 5–10 minutes (switch off at the isolator), then power it back on and attempt one reset. A transient power spike can occasionally corrupt EEPROM data temporarily.
- Check for related fault codes DIY safe
Note whether your boiler has recently shown F.61, F.62, or F.64 as well as F.63. If it has been cycling through multiple electronic fault codes, relay this information to your engineer — it strongly suggests a PCB-level problem and will help speed up diagnosis.
- Call a Gas Safe registered engineer for full diagnosis Gas Safe engineer
F.63 requires professional diagnosis. An engineer will inspect the PCB for visible damage, test the wiring harness and connector integrity, check the NTC thermistors on the flow and return pipes, and assess whether the board needs to be reconfigured or replaced. Gas valve testing may follow if the board appears functional. Do not attempt to access or replace the PCB yourself — this is not a homeowner repair.
Parts you may need
- Main PCB (control board) — Vaillant ecoTEC compatible · from £220
- NTC flow thermistor · from £18
- NTC return thermistor · from £18
- Wiring harness / connector loom · from £45
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 £350–£450, depending on the underlying cause.
Frequently asked questions
Can I fix a Vaillant F.63 fault myself?
No — this is firmly an engineer-only fault. The F.63 error relates to the boiler's PCB and EEPROM, which are core electronic components. Working on these requires specialist diagnostic equipment and, because the PCB controls the gas valve and other safety-critical parts, any incorrect intervention could create a dangerous situation. A Gas Safe registered engineer must carry out the diagnosis and any repair.
How much does it cost to fix a Vaillant F.63 fault in the UK?
Most homeowners pay in the region of £350–£450 all-in (parts and labour) when a PCB replacement is needed, which is the most common outcome. Bear in mind that many general heating engineers may not carry a Vaillant PCB as a stock part, so a second visit is sometimes needed once the part is ordered — using a Vaillant-specialist engineer can avoid this. In rare cases where the fault turns out to be a wiring or thermistor issue rather than a board replacement, costs will be lower, typically £100–£200.
My boiler keeps switching between F.61, F.62, F.63, and F.64 — why?
These four fault codes are all related to PCB and electronic communication failures on Vaillant ecoTEC boilers. A single failing component — most often the main control board — can cause the boiler to display any or all of them at different times. If you are seeing a pattern of these codes, it is a strong indicator of a PCB fault, and you should stop resetting the boiler and arrange for a Gas Safe engineer to inspect it promptly.
Is it worth replacing the PCB on an older Vaillant boiler?
That depends on the boiler's age and overall condition. If your ecoTEC is under 8–10 years old and otherwise in good shape, a PCB replacement at £350–£450 is usually worthwhile. On a boiler that is 12 years or older, or one that has had several repairs recently, the cost of a new board may not represent good value — it is worth getting a quote for a replacement boiler at the same time, so you can make an informed decision. Your Gas Safe engineer should be able to advise you.