Baxi 600 Combi 2 A.02.55 warning: incorrect or missing serial number

If your Baxi 600 Combi 2 shows A.02.55, Baxi describes the warning as “Incorrect or missing serial number”. This refers to identity information recognised by the boiler’s control system. It does not mean you should alter the physical label on the boiler.

The warning may appear while the boiler continues to provide some heating or hot water, or it may coincide with unreliable operation. Record the complete code and arrange professional attention if it persists. The display does not identify which control, setting, or component is responsible.

What does Baxi A.02.55 mean?

Baxi lists A.02.55 for its Combi 2 and System 2 boiler group, which includes the Baxi 600 Combi 2. The exact manufacturer wording is “Incorrect or missing serial number”.

Modern boiler controls use stored identification and configuration information so the appliance can recognise the correct model and operate with the appropriate settings. A.02.55 means expected serial-number information is absent or is not accepted as correct.

This is different from a damaged sticker or an unreadable printed label. The external data label identifies the appliance for owners and engineers, while the warning concerns information the boiler control expects to recognise. Do not write on, remove, replace, or alter the physical label.

What might you notice?

The warning can appear with several different behaviours. The boiler may run, may refuse a demand, or may behave inconsistently after being switched on. Heating and hot water can both be relevant because the Baxi 600 Combi 2 provides both from the same appliance.

Note when the code first appeared. It is useful to know whether it followed a service visit, control replacement, electrical interruption, previous repair, or a period when the boiler was switched off. Those details help an engineer understand the sequence, but they do not prove what caused the warning.

Safe information to record

You can prepare useful information without removing any covers:

• Take a clear photo of A.02.55 on the display.
• Record whether heating, hot water, or both still work.
• Note whether the code appears immediately at start-up or after a demand.
• Write down any recent power cut, service, control work, or boiler repair.
• Record the exact boiler model.
• If an identification label is visible from outside the closed boiler, photograph it without moving or opening anything.

Do not search inside the appliance for a label. If the serial number is not visible externally, leave that step for the attending engineer. The code itself is enough to begin a professional check.

What should you not do?

Do not enter installer menus, attempt to type in a serial number, copy identity information from another boiler, or use values found in an online discussion. Boiler identification and configuration data must match the exact appliance.

Do not remove the casing, touch a circuit board, disconnect plugs, test wiring, or measure voltage, resistance, or continuity. Do not replace a control board based only on A.02.55. The warning describes a data problem but does not prove that any single component has failed.

Avoid factory resets or programming procedures. They can remove settings, create further warnings, or make the original sequence harder to understand.

Can you reset the warning?

One ordinary user reset can be considered only if the Baxi user guide for your exact model permits it and you can use the external control normally. A reset after a brief power interruption may allow the control system to restart cleanly.

If A.02.55 returns, stop resetting the boiler. Repeated resets cannot restore genuinely missing or incorrect identity information and may hide the circumstances that help an engineer trace the issue.

What can be behind A.02.55?

Possible categories include identity information that has not been stored correctly, data that does not match the appliance, an interrupted configuration process, or a problem affecting the control system’s ability to read the expected information.

The code may appear after previous work, but that timing does not establish responsibility or identify a part. It can also appear without any recent intervention. An engineer must compare the appliance identity, installed controls, and stored information using Baxi’s technical process.

What will an engineer check?

A qualified engineer can confirm the exact boiler model and appliance identity, inspect the relevant control history, and check whether the stored information matches the unit. They can also consider whether another fault or interrupted process caused the warning to appear.

If information needs correcting, the engineer can follow the manufacturer’s authorised procedure and then verify that heating, hot water, and safety functions operate normally. Internal boiler work and any gas-appliance checks must remain with a suitably qualified professional.

When should you arrange repair?

Arrange help if A.02.55 remains after one permitted reset, returns after apparently clearing, or affects heating or hot water. The warning also deserves attention when the boiler seems to work, because incorrect identification data can interfere with normal control behaviour.

Give the engineer the display photo, boiler model, any externally visible label photo, and a note of recent work or power interruptions. Do not send or post a full serial number publicly; share appliance-identifying information only with the company handling the repair.

Gas and carbon monoxide safety

A.02.55 is an identity-information warning. It does not itself confirm a gas leak or carbon monoxide. Separate warning signs always take priority. If you smell gas, suspect carbon monoxide, hear a carbon monoxide alarm, notice unusual fumes, or see scorching, stop using the appliance, get fresh air, leave when necessary, and follow current Gas Safe emergency advice. Do not inspect inside the boiler.

Quick answers

Does A.02.55 mean the sticker is missing?

Not necessarily. The warning concerns serial-number information recognised by the boiler, not simply the condition of an external label.

Can I enter the serial number myself?

No. Do not use installer menus or copy values from elsewhere. Identity data must match the exact appliance and should be handled through the manufacturer’s professional process.

Does the control board need replacing?

The code alone does not prove that. Stored information, configuration history, and the control system need checking before parts are considered.

Can the boiler continue working?

Some operation may remain, but behaviour can vary. Record what works and arrange professional attention if the warning persists or returns.