Chaffoteaux 302 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 302 fault code mean?
Fault code 302 on a Chaffoteaux boiler indicates that the two internal electronic boards — commonly referred to as the GP board and the GIU board — have lost communication with each other. This sits within a broader group of electronic board faults (codes 301 to 307), each pointing to a different aspect of PCB-related trouble. Code 302 specifically flags a breakdown in the internal communication link between these two boards, rather than a straightforward main board failure (which would typically show as code 303 or 307). It is not related to code 309 (a gas command fault) or 3P9 (a routine service reminder). When 302 appears, the boiler will usually lock out and stop functioning until the underlying cause is addressed.
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
- Internal water leak causing moisture ingress Common
A leak from the pump, a cracked heat exchanger, or a weeping joint inside the boiler can allow moisture to track along wiring and reach the PCB. Water ingress into the electronic boards is one of the most destructive causes of a 302 fault and can render the board unrepairable.
- Loose or corroded wiring connections Common
All major boiler components connect back to the PCB via a network of wiring looms and connectors. A connector that has worked loose over time, or terminals that have corroded, can interrupt the communication signal between the two boards and trigger this code.
- Electrical surge or power spike Sometimes
A sudden spike in the mains supply — from a power cut restoring, a nearby lightning strike, or a faulty consumer unit — can damage the sensitive circuitry on one or both internal boards, causing them to lose the ability to communicate.
- Component wear and age-related failure Sometimes
Over many years of thermal cycling, solder joints and electronic components fatigue. What may begin as an intermittent fault or flickering display can eventually develop into a persistent 302 lockout as the boards degrade beyond self-recovery.
How to fix it
- Attempt a single boiler reset DIY safe
Locate the reset button on your Chaffoteaux boiler (usually marked with a flame or reset symbol) and press it once, following the instructions in your user manual. Occasionally a 302 fault is a one-off communication glitch that clears on reset. If the fault returns immediately or within a short time, do not reset again — repeated resets can place additional stress on an already compromised board. Switch the boiler off at the programmer or room thermostat and contact a Gas Safe engineer.
- Check for visible signs of a water leak around the boiler DIY safe
While you wait for an engineer, have a look at the area around and beneath the boiler casing for any drips, staining, or damp patches. Do not remove the boiler casing yourself. If you can see an active leak, turn off the boiler and, if you are confident doing so, isolate the water supply to the boiler using the service valves. Inform the engineer before they arrive — moisture ingress is a key cause of this fault.
- Have a Gas Safe engineer inspect the wiring and connectors Gas Safe engineer
A registered engineer will remove the boiler casing and systematically check all wiring looms and connectors linking the GP and GIU boards. Loose pins, corroded terminals, or chafed cables are checked and re-secured or replaced before any more expensive component is condemned. This step can resolve the fault without the need for a new board.
- Have the engineer diagnose and replace the faulty PCB if required Gas Safe engineer
If wiring checks out and the fault persists, one or both internal boards will need to be replaced. PCB replacement on a Chaffoteaux boiler requires specialist knowledge and appropriate test equipment. The engineer will likely need to source the specific board — which may not be in stock — so allow time for the part to be ordered. Once fitted, the board must be tested through a full firing cycle before the job is signed off.
- Consider the boiler's age before authorising a PCB repair DIY safe
Chaffoteaux boilers typically have a working life of around 10 to 15 years with regular servicing. If your boiler is approaching or beyond that age and the PCB replacement cost is more than half the price of a new boiler installation, discuss with your engineer whether a full replacement might offer better long-term value, improved efficiency, and a new manufacturer warranty.
- Call a Gas Safe registered engineer Gas Safe engineer
All work beyond a single reset on a 302 fault requires a Gas Safe registered engineer. PCB diagnosis, wiring repairs, and board replacement are not tasks a homeowner should attempt. You can find a registered engineer at gassaferegister.co.uk or through a reputable local heating company.
Parts you may need
- Chaffoteaux PCB (main / GIU board) · from £280
- Chaffoteaux GP board · from £160
- Wiring loom and connector set · from £35
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 £450–£700, depending on the underlying cause.
Frequently asked questions
Can I fix a Chaffoteaux 302 fault myself?
The only action a homeowner should take is a single reset. If the fault clears and stays away, monitor the boiler over the next day or two. If 302 returns, all further work — inspecting wiring, diagnosing board faults, and replacing the PCB — must be carried out by a Gas Safe registered engineer. Boiler PCB work is not DIY territory, both for safety reasons and because incorrect handling can cause further damage to an expensive component.
How much does it cost to replace a Chaffoteaux boiler PCB in the UK?
For most Chaffoteaux models, the PCB itself typically costs between £160 and £400 depending on which board has failed and whether it needs to be sourced directly from the manufacturer. Labour for diagnosis and fitting usually adds £150 to £300, bringing the typical total to around £450 to £700. Note that the engineer may not carry your specific board in their van, so factor in a wait of a few days while it is ordered. If the repair quote is approaching or exceeding half the cost of a new boiler, it is worth getting a replacement boiler quote for comparison.
What is the difference between Chaffoteaux fault codes 301, 302, 303, and 307?
Codes 301 to 307 all relate to electronic board faults on Chaffoteaux boilers, but each points to a slightly different issue. Code 302 specifically flags a loss of communication between the GP and GIU internal boards. Codes 303 and 307 are more indicative of a general main board failure rather than an inter-board communication issue. Code 301 covers other board anomalies within the same family. In practice, the diagnostic steps overlap significantly — a Gas Safe engineer will work through wiring, connectors, and then the boards themselves regardless of which code in the 301–307 range is displayed.
My Chaffoteaux boiler keeps showing 302 after resetting — is it safe to keep resetting it?
No. If the 302 fault returns after a single reset, you should stop resetting the boiler. Repeatedly forcing the boiler through its ignition sequence when an internal board communication fault is present can put additional strain on the already affected components and risks making the damage worse. Switch the boiler off and arrange for a Gas Safe engineer to inspect it. In the meantime, if you have no heating or hot water, an immersion heater (if fitted) or portable electric heaters can be used safely while you wait.