Chaffoteaux 301 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 301 fault code mean?
Fault code 301 on a Chaffoteaux boiler signals an EEPROM error on the main control board (PCB). The EEPROM is a small memory chip embedded within the PCB that holds the boiler's factory configuration and operating parameters. When this chip becomes corrupted or fails, the boiler cannot read the settings it needs to run safely and will lock out completely. Codes 301 through 307 all relate to anomalies on the main PCB — ranging from communication faults to internal short circuits — but 301 specifically points to the EEPROM memory component. Expect no heating and no hot water until the fault is 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
- PCB or EEPROM failure due to power surge Common
A sudden voltage spike or brief power cut can damage sensitive electronic components on the PCB, including the EEPROM chip and protective varistors. When power is restored the EEPROM may have lost its factory data, triggering code 301 immediately on startup. This is one of the most direct causes and typically requires a full PCB replacement.
- Water ingress or internal leak onto the PCB Common
Even a small drip from a pump seal, heat exchanger, or nearby pipe joint can track moisture onto the control board. Water causes short circuits and corrosion on the PCB that can corrupt the EEPROM or damage the board beyond repair. This is one of the most damaging and common routes to an electronic fault.
- Loose or corroded wiring connections to the PCB Sometimes
Vibration over time, or poor connections from a previous repair, can leave wiring terminals partially detached from the PCB. This can cause intermittent signal errors that the board logs as an EEPROM or internal fault. An engineer will check all low-voltage connectors as a first step before condemning the board.
- Faulty sensor sending corrupt data to the PCB Sometimes
Although the code points directly to the PCB, a sensor feeding incorrect data — such as a failed NTC thermistor or a damaged flow sensor — can occasionally cause the board to log an internal fault code. An engineer will rule out sensor issues during diagnosis before replacing the board.
- Age-related component degradation Rare
On older Chaffoteaux boilers approaching or beyond ten years of service, electrolytic capacitors and solder joints on the PCB naturally degrade. This can eventually cause the EEPROM or surrounding circuitry to malfunction even without an obvious external trigger.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Chaffoteaux boiler (usually marked with a flame symbol or labelled 'Reset'). Press and hold for the time specified in your user guide, then wait a few minutes for the boiler to attempt a restart. If the fault clears and the boiler runs normally, monitor it over the next day. If code 301 returns, do not keep resetting — repeated resets will not fix an EEPROM fault and can mask useful diagnostic information for the engineer.
- Check for any obvious signs of a water leak near the boiler DIY safe
Without removing any panels, inspect the area immediately around the boiler casing and the condensate pipe for damp patches, drips, or corrosion staining. If you find an active leak, turn off the boiler and water supply and note the location — this information will help the engineer prioritise their investigation.
- Verify the gas and electricity supplies are normal DIY safe
Confirm other gas appliances in the property (hob, fire) are working normally, which rules out a gas supply interruption. Check the boiler's fused spur switch and your consumer unit for any tripped breakers. A recent power cut or surge coinciding with the fault appearing is worth mentioning to the engineer.
- Contact a Gas Safe registered engineer for diagnosis Gas Safe engineer
Code 301 is an internal PCB/EEPROM fault that cannot be resolved without opening the boiler casing and using diagnostic equipment. A Gas Safe engineer will test each input and output on the board, check wiring harnesses and connectors, inspect for moisture damage, and determine whether the EEPROM needs reprogramming or the full PCB requires replacement. Do not attempt to open the boiler casing or work on any internal components yourself.
- PCB repair or replacement by a Gas Safe engineer Gas Safe engineer
If the engineer confirms the PCB or EEPROM is faulty, they will source a compatible replacement board for your Chaffoteaux model. The new PCB will need to be correctly configured for your boiler's parameters before refitting. On older boilers, the engineer may also advise whether a full boiler replacement is more economical than a major PCB repair — particularly if the boiler is over ten years old or has additional worn components.
Parts you may need
- Chaffoteaux main PCB (control board) · from £320
- NTC thermistor sensor · from £25
- Wiring harness / loom · from £55
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–£600, depending on the underlying cause.
Frequently asked questions
Can I fix Chaffoteaux fault code 301 myself?
No. Code 301 is an internal PCB or EEPROM fault that requires a Gas Safe registered engineer. The only safe DIY steps are a single reset attempt and checking for obvious external leaks or supply issues. Opening the boiler casing to work on the control board is not safe for an unqualified person and may invalidate any remaining warranty.
How much does it cost to repair a Chaffoteaux 301 fault in the UK?
Most homeowners pay in the region of £350 to £600 all-in for diagnosis, parts, and labour. The engineer's call-out and diagnostic fee is typically £60 to £100, and a replacement PCB for a Chaffoteaux boiler usually costs £180 to £350 for the part alone. In rare cases — for example where water damage has affected multiple components — the total could exceed £600, and at that point it may be worth comparing the cost against a new boiler installation.
What is the difference between Chaffoteaux fault codes 301, 302, and 303?
Fault codes 301 to 307 all indicate an anomaly on the main PCB. Code 301 specifically flags an EEPROM memory error — a failure or corruption of the chip that stores the boiler's configuration. Codes 302 to 307 cover other internal PCB communication or circuit faults. In practice, the diagnostic approach and likely repair (PCB inspection or replacement) is similar across all these codes, and a Gas Safe engineer will use the full code together with their diagnostic tools to identify the precise fault.
My Chaffoteaux boiler is over 10 years old and showing code 301 — should I repair or replace it?
Chaffoteaux boilers typically have a service life of around 10 to 15 years. If your boiler is in that range and a PCB replacement is going to cost £400 or more, it is worth getting a quote for a new boiler at the same time. As a rough guide, if the repair cost is more than half the price of a comparable new installation, replacement often works out better value in the long run — especially given the improved efficiency of modern condensing boilers. Ask your Gas Safe engineer for their honest assessment.