Baxi 5 Red Flashes Fault Code: Causes, Fixes & Repair Costs
What does the Baxi 5 Red Flashes fault code mean?
Five red flashes on a Baxi boiler indicate a Parameter Storage Unit (PSU) error — a fault within the boiler's control electronics that prevents normal operation. Unlike the 5 green flashes code, which can sometimes self-resolve, the 5 red flashes version is a hard fault: the boiler has detected a permanent problem with its parameter storage or the PCB (printed circuit board) that controls it, and it will not clear on its own. A Gas Safe engineer is needed to diagnose and rectify this fault. It is also worth knowing that a malfunctioning PCB can sometimes display incorrect fault codes, so the engineer may find a slightly different underlying issue once they investigate.
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 failure or damage Common
The printed circuit board is the boiler's main control unit. If it suffers a component failure, power surge damage, or internal corruption, it can trigger a PSU error and display 5 red flashes. This is the most frequently identified root cause when an engineer investigates this code.
- Channel Service Unit (CSU) time-out Common
The CSU is a function within the boiler's control electronics that manages parameter storage. If it times out — due to age, firmware issues, or an underlying electrical fault — the boiler logs a permanent PSU error and locks out.
- Wiring fault or loose connection Sometimes
Damaged, corroded, or poorly seated wiring between the PCB and other components can disrupt communication within the control system. This can manifest as a parameter or storage error even when the PCB itself is otherwise intact.
- Software or parameter corruption Rare
In some cases, the boiler's stored parameters can become corrupted — for example following a power cut or voltage spike — leading the boiler to report a PSU fault. An engineer may be able to reprogram or update the boiler's software rather than replacing hardware.
How to fix it
- Do not repeatedly reset the boiler DIY safe
A single reset attempt is reasonable, but 5 red flashes is a hard-lockout fault that is not designed to self-clear. Repeatedly pressing the reset button will not resolve the underlying issue and may make diagnosis harder for the engineer.
- Check the boiler's display for any additional information DIY safe
Note exactly what is shown on the display — the number of flashes, any accompanying text or codes, and whether the fault appeared suddenly or after a power interruption. This information helps the engineer narrow down the cause before they arrive.
- Check that the mains electrical supply is stable DIY safe
Confirm the boiler's fuse or circuit breaker has not tripped and that other appliances on the same circuit are working normally. A voltage spike or power cut can sometimes corrupt parameter storage and trigger this fault.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
A qualified engineer will inspect the PCB, CSU, and associated wiring to determine whether the fault lies in the parameter storage unit itself, a damaged PCB, or a wiring issue. They will carry test equipment to confirm the diagnosis before ordering parts, typically completing the repair on the same visit.
- Engineer to test and replace the PCB or repair wiring as required Gas Safe engineer
If the PCB is confirmed faulty, the engineer will source a compatible replacement board for your Baxi model, fit it, and re-commission the boiler. If a wiring fault is found instead, they will repair or replace the affected connections. In some cases, reprogramming the boiler's parameters is sufficient without a full PCB swap.
Parts you may need
- Baxi PCB (main circuit board) · from £180
- Wiring loom / control harness · from £45
- Parameter storage / CSU module (where separate) · from £60
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 £200–£420, depending on the underlying cause.
Frequently asked questions
Can I reset a Baxi 5 red flashes fault myself?
You can try a single reset, but this fault is classified as a hard lockout that will not clear through resetting alone. Unlike some other Baxi fault codes, the 5 red flashes PSU error requires an engineer to identify and fix the underlying cause before the boiler will run normally again.
Is the PCB always at fault when I see 5 red flashes?
It is the most common cause, but not the only one. A wiring fault, a CSU time-out, or even parameter corruption from a power surge can produce the same code. An engineer will test each possibility before replacing parts — replacing a PCB unnecessarily is expensive, so a proper diagnosis matters. PCB replacement typically costs £180–£250 for the part alone, plus labour.
How much does it cost to fix Baxi 5 red flashes in the UK?
Most homeowners pay in the region of £200–£420 for diagnosis and repair, which usually covers the engineer's call-out and either a wiring fix or a PCB replacement. If the PCB needs replacing, the part itself can cost £180 or more depending on the Baxi model. Very old boilers where parts are difficult to source may cost more — in that situation, your engineer may recommend weighing up repair costs against a new boiler installation.
My Baxi boiler is showing 5 red flashes after a power cut — is that related?
Yes, this is a known trigger. A sudden loss of mains power or a voltage spike can corrupt the boiler's stored parameters and cause a PSU error. The fix is the same — a Gas Safe engineer will need to attend — but in post-power-cut cases there is a reasonable chance the parameters can be reprogrammed without replacing the PCB, which would keep costs lower.