If your Baxi boiler shows A.02.54, Baxi’s official description is: “OpenTherm bus power supply error.” The boiler has detected a problem with the power supply used by its OpenTherm communication connection.
This is not a household mains-power instruction and it is not safe to investigate boiler terminals yourself. Note the exact code, check only visible user controls, and arrange professional repair if the message remains or returns.
What does Baxi A.02.54 mean?
OpenTherm is a communication system that compatible thermostats and boilers can use to exchange information and control heating and hot water. The “bus” is the communication link. A.02.54 reports a power-supply error associated with that link.
The code does not prove that the thermostat itself is faulty. It also does not identify whether the issue is in a control, connection, boiler electronics or configuration. An engineer must assess the exact installed system before deciding what repair is required.
Which Baxi boilers list A.02.54?
Baxi includes A.02.54 in the current Combi & System 2 error-code group. The listed models are the Baxi 200, 400, 600 and 800 Combi 2, Baxi Assure 500 Combi 2, Baxi 600 and 800 System 2, and Baxi Assure 500 System 2.
Not every home uses the same control arrangement, even when the boiler model matches. Check your model name and keep details of the room control or thermostat you normally use. Do not assume an OpenTherm accessory is fitted solely because this code appears.
What is OpenTherm?
Baxi describes OpenTherm as the “language” compatible thermostats and boilers use to talk to each other and control heating and hot water. This allows more information to pass between compatible devices than a simple on/off request.
For a homeowner, the safe takeaway is straightforward: A.02.54 concerns that communication system’s power supply. It does not invite voltage measurements, wiring changes or terminal checks.
What might you notice?
You may find that heating does not respond to the room control, the control display looks different, or the boiler shows the code while hot water behaves differently. These observations are useful, but they do not prove which device or connection is responsible.
Record whether the thermostat display is on, whether it shows a simple battery warning, and whether the issue followed a power interruption or recent control work. Follow only the user instructions for the visible control.
Safe checks for A.02.54
- Write down the full code as A.02.54.
- Confirm the exact boiler model from external product information.
- Note the make and model of the normal room control if visible.
- Check whether that control has a working display or a clear user-level battery warning.
- Record whether heating and hot water respond normally.
- Note any other code shown before or after A.02.54.
Do not remove the boiler casing, open the thermostat receiver, inspect terminals, test voltage or polarity, alter wiring, bypass the control, change installer settings, attempt pairing workarounds or replace the PCB. These are not safe homeowner actions.
Should you reset the boiler or thermostat?
Reset instructions vary by appliance and control. Follow the exact user guides only. If your Baxi boiler guide explicitly instructs a homeowner reset for the situation, use it once. Do not repeatedly reset the boiler or cycle power in an attempt to force the communication link back.
If a battery-powered user control displays a clear low-battery warning, follow its own manual. That does not guarantee the boiler code will clear, because A.02.54 specifically concerns the OpenTherm bus power supply and still may require professional attention.
Can you use the boiler?
Follow the model-specific user guide and do not bypass the room control. If heating is unavailable, the code persists or operation is unpredictable, arrange repair. If another safety warning appears, switch the boiler off using the normal user control where safe.
If you smell gas, suspect carbon monoxide, feel unwell or a carbon-monoxide alarm sounds, treat that as an emergency. Follow Gas Safe Register advice and contact the gas emergency service rather than continuing control checks.
What will an engineer check?
An engineer will confirm the boiler and control models, establish whether OpenTherm is part of the installation, and assess the communication link and power supply using the correct manufacturer information. The code guides those checks but is not a complete component diagnosis.
Tell the engineer whether the control display remained on, when the code began and whether there was a power cut or recent work. That information is useful without you touching electrical connections.
A.02.54 is affecting your heating controls?
Book a fixed-price boiler repair aimed at fixing the fault, with a clear booking price before the visit.
Quick answers about Baxi A.02.54
What does A.02.54 mean?
It means the OpenTherm bus has a power-supply error.
What is OpenTherm?
It is a communication language compatible thermostats and boilers use to control heating and hot water.
Does A.02.54 prove the thermostat is faulty?
No. The exact installed control system must be assessed.
Can I test the OpenTherm wiring?
No. Do not open terminals, measure voltage, change polarity or alter wiring.
Who should repair A.02.54?
A suitably qualified Gas Safe registered engineer familiar with the installed controls.