The Baxi A.02.55 code means “Incorrect or missing serial number.” It is a technical identification-data message used by the boiler’s controls. It does not tell you that the printed label on the outside of the boiler has definitely fallen off, and it does not prove that any one internal component has failed.
If your display shows A.02.55, write down the code exactly as it appears and note whether the heating and hot water are still working. The safest next step is to check the user information for your exact Baxi model and arrange professional help if the message remains.
What does Baxi A.02.55 mean?
Baxi’s current error-code information defines A.02.55 as an incorrect or missing serial number. In this context, the serial number is part of the identifying information associated with the appliance and its controls. The code is not an invitation to enter, copy, change or invent a serial number yourself.
The same code can appear on several current Baxi ranges, including Baxi 200, 400, 600 and 800 Combi 2 boilers, Baxi Assure 500 Combi 2, Baxi 600 and 800 System 2, and Baxi Assure 500 System 2. Always match the advice to the full model name on your own appliance because controls and reset arrangements vary.
Is the serial number label missing?
Not necessarily. A boiler normally has an external product label carrying model and serial information, but A.02.55 refers to information recognised by the boiler’s control system. A label can still be physically present while the display reports this code. Equally, a damaged or unreadable external label does not by itself explain what is happening internally.
If the label is easy to see without removing a panel, you can photograph it for the engineer. Do not peel it off, alter it or copy details from another appliance. The engineer may use the boiler’s model and serial information alongside the code, its history and safe tests to determine the correct repair.
What can cause an incorrect or missing serial-number message?
The public fault description does not name a single failed part, so it is best not to jump to a conclusion. The message may follow installation or commissioning work, a previous repair, a control-component change, or a problem with the way appliance information is stored or read. Those possibilities require trained checks and are not homeowner repair tasks.
A.02.55 is therefore different from a straightforward operating setting such as the temperature selected on the front panel. Changing the room thermostat, programmer or heating schedule is unlikely to correct technical appliance identity data.
What should you check before booking a repair?
You can collect useful information without opening the boiler:
- Confirm that the display says A.02.55, including the dots and leading zero.
- Note the complete Baxi model name from an accessible external label or your paperwork.
- Record whether heating, hot water or both are unavailable.
- Note whether the code appeared after installation, servicing, repair work or a power interruption.
- Write down any other messages that alternate with A.02.55.
- Keep a photograph of the display and any readable external product details.
This information helps the attending engineer arrive with a clearer picture of the boiler and the circumstances around the fault.
Can you reset a Baxi A.02.55 code?
Only use the normal reset control if the user guide for your exact model tells you how to do so. A single reset may clear a temporary interruption, but repeatedly resetting the boiler will not correct missing or inconsistent appliance data. If A.02.55 returns, remains on screen or prevents normal operation, stop resetting and arrange a repair.
Avoid installer menus, commissioning settings and factory-reset options. Do not open the casing or touch internal wiring, connectors, memory devices or the main control board. These checks belong to a suitably qualified Gas Safe registered engineer.
Is A.02.55 dangerous?
The code itself describes a serial-number information problem; it is not Baxi’s published description of a gas leak or carbon-monoxide alarm. Even so, a boiler showing a persistent technical code should not be dismantled or bypassed.
If you smell gas, suspect carbon monoxide, feel unwell around the appliance or hear a carbon-monoxide alarm, turn the appliance off only if it is safe to do so, ventilate the property, leave the area and follow the current emergency advice from the National Gas Emergency Service and Gas Safe Register. Do not wait for an ordinary repair appointment.
Who should repair a Baxi A.02.55 fault?
A Gas Safe registered engineer with suitable boiler competence should investigate the code. They can confirm the precise model, check the appliance information safely and decide what corrective work is appropriate. A fault code is a starting point for trained testing, not proof that a particular board or component must be replaced.
Keep the boiler closed and avoid buying parts based on the code alone. A correct repair depends on the exact appliance, its history and the engineer’s findings.
Need help with a Baxi A.02.55 code?
Book a fixed-price boiler repair aimed at fixing the fault, with the booking price clear before the visit.
Quick answers about Baxi A.02.55
What does A.02.55 mean on a Baxi boiler?
It means “Incorrect or missing serial number,” according to Baxi’s current fault-code information.
Does A.02.55 mean the sticker has fallen off?
No. The code concerns serial-number information recognised by the boiler controls. The external label may still be present.
Can I enter the boiler serial number myself?
No. Do not enter, change or copy technical identity data through installer settings. Leave that work to a suitably qualified engineer.
Will switching the boiler off and on fix A.02.55?
A model-approved reset may clear a temporary interruption, but a code that returns needs professional attention. Repeated resets are not a repair.
Can I keep using the boiler?
Follow the user guide for your exact model. If the boiler is locked out, behaves unusually or the code persists, stop trying to restart it and arrange a repair.
What information should I give the engineer?
Provide the exact A.02.55 display, full model name, any readable external serial details, the status of heating and hot water, and whether recent work or a power interruption came before the message.