Baxi 5 Green Flashes Fault Code: Causes, Fixes & Repair Costs
What does the Baxi 5 Green Flashes fault code mean?
When your Baxi boiler displays 5 green flashes, it is signalling a parameter error on the PSU (Parameter Storage Unit) or PCB (Printed Circuit Board). In plain terms, the boiler's control board — the electronic brain that coordinates every part of the heating system — has detected a configuration or data mismatch. Baxi classifies this as a temporary fault that can clear on its own, but if the flashing persists after a reset or two, a deeper PCB or PSU problem is likely at fault and will need professional attention.
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
- Temporary software or parameter glitch Common
The most common scenario. The PSU or PCB stores configuration data about the boiler's settings, and occasionally a transient power fluctuation or communication hiccup causes the stored parameters to become inconsistent. The boiler flags this as a fault and may clear it automatically, or after a manual reset.
- PCB fault or component failure Sometimes
If the 5-flash code keeps returning after resets, the control board itself may be developing a fault. Individual components on the PCB — capacitors, relays, or solder joints — can degrade over time, especially in older boilers or those that have been exposed to prolonged overheating.
- Power surge damage Sometimes
A sharp voltage spike on the mains supply — from a nearby lightning strike or the National Grid switching — can damage sensitive electronics on the PCB or PSU, causing corrupted parameters and persistent fault codes.
- Overheating of the PCB due to poor ventilation Rare
If the boiler cupboard or plant room is poorly ventilated, or if the heat exchanger is running excessively hot, the ambient temperature around the PCB rises. Sustained high heat degrades electronic components and insulation, eventually leading to parameter errors or board failure.
How to fix it
- Reset the boiler (first attempt) DIY safe
On most Baxi models, turn the selector dial or press the reset button — usually marked 'R' — and hold it for approximately 5 seconds, then release. The display should return to showing the flow temperature and normal operation. Wait a few minutes to confirm the fault has cleared before considering the job done.
- Observe whether the fault returns DIY safe
If the boiler runs normally for a while and then the 5 green flashes reappear, attempt one further reset. It is reasonable to reset up to 2–3 times, but repeatedly resetting without the fault clearing is not a solution — it can mask an underlying problem.
- Check your mains power supply DIY safe
Confirm the boiler's fused spur is switched on and that no fuses have blown in the consumer unit. If other appliances on the same circuit were affected, an electrician may need to investigate a wiring or surge issue before the boiler fault is addressed.
- Inspect visible wiring and connectors (visual check only) DIY safe
Without removing any panels or touching internal components, look for any obviously scorched, melted, or disconnected cables around the boiler's external controls. Do not open the boiler casing or interfere with internal wiring — this step is a visual external check only.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the 5 green flashes return after resetting, or if the boiler fails to fire up and restore heating or hot water, a qualified Gas Safe engineer needs to diagnose the PCB and PSU. They will carry out component-level testing, check for error data stored in the board's memory, and advise whether repair or replacement is the better option. PCB work is not DIY territory — incorrect handling can damage the board further or create a safety risk.
Parts you may need
- Replacement PCB (Baxi-compatible) · from £220
- PSU (Parameter Storage Unit) · from £85
- PCB connector harness / wiring 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 £150–£450, depending on the underlying cause.
Frequently asked questions
Can the Baxi 5 green flashes fault clear itself without any action?
Yes, in many cases it can. Baxi themselves describe this as a temporary fault that the system may self-reset. If a minor power fluctuation caused the parameter error, the boiler may resume normal operation on its own within a few minutes. That said, if it happens repeatedly, it should not be ignored — recurring faults usually point to a PCB that needs professional inspection.
How much does it cost to fix the Baxi 5 green flashes fault in the UK?
If the fault clears on its own or with a reset, there is no cost at all. If an engineer is needed, you can typically expect to pay £60–£100 for a diagnostic visit, and £150–£450 all-in if a repair involves replacing the PSU module or carrying out PCB component-level work. Full PCB replacement — which is less commonly needed — tends to cost more, often £400–£650 including parts and labour. If your boiler is older than 10–12 years, it may be worth discussing replacement with your engineer, as PCB costs on an ageing boiler can outweigh the benefit.
Is a 5-green-flash fault on a Baxi boiler dangerous?
Not directly. Unlike a gas pressure fault or a carbon monoxide-related lockout, a parameter error on the PSU or PCB does not indicate a gas leak or combustion problem. The main consequence is that the boiler may stop working until the fault is resolved. However, you should always make sure your carbon monoxide detector is working, and if you ever smell gas or suspect a leak, leave the property and call the National Gas Emergency Service on 0800 111 999 immediately.
My Baxi boiler shows 5 green flashes after a power cut — is that normal?
Yes, this is a recognised pattern. Power interruptions — especially if accompanied by a voltage spike when supply is restored — can corrupt the parameters stored on the PSU or PCB, triggering the 5-flash code. A reset will resolve it in most cases. If it happens every time the power is disrupted, an engineer can fit a surge-protection device to reduce the risk of recurrence.