Baxi 6 Green Flashes Fault Code: Causes, Fixes & Repair Costs
What does the Baxi 6 Green Flashes fault code mean?
Six green flashes on a Baxi boiler indicate a miscellaneous or unspecified error, sometimes linked to a fault within the combustion control unit. Unlike a solid red lockout, this is classified as a temporary fault that can self-reset — meaning the boiler may recover on its own without any intervention. That said, if the flashing persists or keeps returning, it can point to an underlying issue such as a PCB problem or a component that needs professional attention. To put it in context, Baxi uses a green flash sequence to communicate different states: 1 flash means the target temperature has been reached (normal), 3 flashes indicate a temporary flame loss, 4 flashes signal a communication error between the PCB and control board, 5 flashes point to a parameter error on the PSU or PCB, and 6 flashes represent this catch-all miscellaneous fault. All of the multi-flash codes from 3 upwards are designated temporary errors that should self-reset, but recurring codes always warrant investigation.
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
- Transient or temporary system glitch Common
A momentary disruption — such as a brief power fluctuation, a brief dip in gas supply pressure, or the boiler completing a start-up sequence after being switched off — can trigger 6 green flashes without any lasting fault. The boiler's control system flags the anomaly and will typically clear itself within a few minutes.
- PCB fault or malfunction Common
The printed circuit board governs every function on the boiler. If the PCB develops a fault — through age, moisture ingress, or component failure — it may generate a miscellaneous error code such as 6 green flashes, sometimes without any other obvious symptom. A faulty PCB can also produce misleading codes that do not reflect the true underlying problem.
- Combustion control unit issue Sometimes
The combustion control unit manages the ignition sequence and flame supervision. A fault or degradation within this component can cause the boiler to flag a miscellaneous error. This is more likely on boilers that have not been serviced regularly or are several years old.
- Wiring or internal communication fault Sometimes
Loose connections or damaged wiring between internal components can cause intermittent communication errors that surface as a 6-flash code. Vibration over time, or poor installation, can cause terminals to work loose.
- Boiler overdue a service Sometimes
Accumulated scale, debris, or worn components can cause the boiler to behave erratically and throw miscellaneous fault codes. Regular annual servicing helps prevent this type of vague, hard-to-diagnose fault from developing.
How to fix it
- Wait and observe whether the boiler self-resets DIY safe
Because 6 green flashes is classified as a temporary fault, the first thing to do is simply wait 10–15 minutes, particularly if the boiler has just been switched on after a power cut or a period of inactivity. The control system may clear the fault automatically and resume normal operation. Check whether the flashing has stopped and the boiler is firing normally before taking any further action.
- Check that your gas supply is working DIY safe
Confirm that other gas appliances in your home (such as a gas hob) are working normally. If nothing gas-powered is working, contact your gas supplier — there may be a supply interruption in your area. Do not attempt to investigate gas pipework yourself.
- Attempt a manual reset (once or twice only) DIY safe
On most Baxi models, turn the selector or control dial to the Reset (R) position and hold it for approximately 5–6 seconds. You should hear the boiler attempt to restart. Release the dial and return it to your desired heating setting, then wait a few minutes to see if normal operation resumes. If the fault clears, monitor the boiler over the next day or two. Do not reset the boiler more than two or three times — repeated resets without a resolution can mask a more serious fault and should prompt a call to an engineer.
- If the fault persists or keeps returning, call a Gas Safe registered engineer Gas Safe engineer
Recurring 6 green flashes that do not self-reset and do not clear after a manual reset indicate an underlying fault that requires professional diagnosis. A Gas Safe engineer will use diagnostic equipment to check the combustion control unit, PCB, wiring, and internal components. Do not attempt to open the boiler casing, inspect the PCB, or interfere with gas or electrical components yourself — this work must only be carried out by a qualified Gas Safe registered engineer.
Parts you may need
- PCB (Printed Circuit Board) · from £180
- Combustion control unit / burner control board · from £120
- Ignition lead and electrode assembly · from £35
- Boiler wiring harness · 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 £120–£380, depending on the underlying cause.
Frequently asked questions
Will 6 green flashes on my Baxi boiler clear itself?
In many cases, yes. Baxi classifies this as a temporary fault code that the boiler's control system can self-reset. If the boiler recovers on its own within 10–15 minutes and runs normally afterwards, no further action may be needed. However, if the fault keeps reappearing, that pattern suggests an underlying problem — such as a PCB fault or combustion control issue — that a Gas Safe engineer needs to investigate.
How much does it cost to fix a Baxi boiler showing 6 green flashes?
For most common causes, you should expect to pay roughly £120–£380, which covers a Gas Safe engineer's call-out, diagnosis, and a typical repair such as replacing a wiring connection, combustion control component, or carrying out a full service. If the PCB turns out to be the culprit, parts and labour for a PCB replacement on a Baxi boiler typically run to £300–£450. In more complex scenarios involving both the PCB and the fan, costs can reach £600 or more — but this is the exception rather than the norm.
Is it worth repairing an older Baxi boiler that keeps showing green flash faults?
If your Baxi boiler is more than 8–10 years old and has been throwing repeated fault codes, repair costs can quickly add up. A Gas Safe engineer's honest assessment is the best starting point — if one major component has failed, others on an ageing boiler may not be far behind. In that situation, investing in a replacement boiler is often more economical in the long run than continuing to repair an old one.
What is the difference between all the Baxi green flash codes?
Baxi uses the number of green flashes to indicate different states. One flash simply means the boiler has reached its set temperature — this is completely normal. Three flashes indicate a temporary flame loss. Four flashes signal a communication error between the PCB and the control board. Five flashes point to a parameter error on the PSU or PCB. Six flashes — the code on this page — represent a miscellaneous or unspecified error, sometimes linked to the combustion control unit. All of the multi-flash codes (3 through 6) are designated temporary faults that should self-reset, but any that recur regularly need professional attention.