Baxi 600 System 2 A.02.45 warning: connection error

A.02.45 on a Baxi 600 System 2 means “Connection error”. That is the current description in Baxi’s fault-code information for the Combi 2 and System 2 range. It is a broad warning: it confirms that an expected connection is not working correctly, but it does not identify the failed component on the display.

Your heating may stop responding, work intermittently, or continue with limited symptoms. The useful first step is to record the full code and what the system was doing when it appeared. Avoid guessing which part has failed, because the same warning can require different checks on differently configured systems.

What does Baxi A.02.45 mean?

The boiler monitors the connections it needs in order to work with the system around it. A.02.45 indicates that one of those expected connections has produced an error. The Baxi 600 System 2 is included in the manufacturer’s applicable model group, so this description is relevant to this boiler.

The wording does not state whether the problem is with a control, accessory, cable, connector, configuration, or internal interface. It also does not say that every connected device has failed. An engineer must identify which connection the boiler expected to see and compare that with the equipment fitted at the property.

That is why replacing a thermostat, programmer, or boiler part based on the code alone is not sensible. A part may be working while its connection is interrupted, or the system may be configured to expect something that is not being recognised.

What might happen when the warning appears?

You may find that central heating does not start when requested, that it starts and then stops, or that a separate control no longer changes the boiler’s operation. Hot water performance depends on the wider system, including the cylinder and controls fitted to a system-boiler installation. In some homes the boiler may still appear to operate while displaying the warning.

Record precisely what works. For example, note whether the boiler responds to a normal heating request, whether a programmer screen is powered, and whether any other user-facing device shows a message. If the main symptom is unexplained stopping, our guide to a boiler that keeps turning off can help you record the pattern without opening the appliance.

Safe observations before arranging a repair

Keep every check external and limited to the controls you normally use. The following information is useful:

• Photograph or write down A.02.45 exactly as shown.
• Note whether the warning is permanent or comes and goes.
• Record whether radiators warm up when heating is requested.
• Check visible room controls and programmers for a blank screen or their own message, without removing any covers.
• Remember whether there was a recent power interruption, electrical work, decorating, or a change to heating controls.
• Write down the boiler model and visible control names.

Do not remove the boiler casing, inspect terminals, reconnect cables, bridge contacts, measure voltage or resistance, or enter installer menus. Those actions can create risk, change the evidence, or cause further problems. Even low-voltage-looking controls can be connected to equipment that must be isolated and tested correctly.

Can you reset A.02.45?

If the user guide for your exact Baxi 600 System 2 permits a normal user reset, one reset can be reasonable after a brief power interruption. Follow only the user control instructions and keep the casing closed.

If the warning comes back, do not keep resetting the boiler. A recurring connection error needs investigation. Repeated resets do not repair a poor connection or configuration problem and may make an intermittent pattern less obvious.

What can cause a connection error?

The code’s verified wording supports several broad possibilities, not a single diagnosis. An expected device may no longer be detected; a physical connection may be interrupted; a compatible control or accessory may have lost power; or the system configuration may not match the equipment now connected.

Environmental timing can also be useful without proving the cause. A warning that started after a power cut points the engineer toward the sequence of events, while one that appeared after control work highlights a different area to verify. Neither observation tells you which part to buy.

Because the Baxi 600 System 2 is a system boiler, installations can differ in their cylinders, zone controls, programmers, and other external components. Advice that applies to one home may not apply to another, even when the boiler model is the same.

What will the engineer do?

A qualified engineer will establish which connected equipment the boiler is configured to use, inspect the relevant connections, and test communication or signals in line with Baxi’s technical information. They will also consider whether the warning follows another underlying problem rather than treating the display text as a parts list.

Once the failed connection or configuration issue is confirmed, the engineer can repair or replace only what is necessary and verify normal operation. This work may involve areas behind the boiler casing or connected heating controls, so it is not a homeowner task.

When should you arrange professional help?

Arrange a repair when A.02.45 remains after one permitted reset, returns repeatedly, prevents reliable heating, or coincides with a blank or unresponsive control. An intermittent warning is still worth checking, especially before cold weather makes reliable heating more important.

Provide the engineer with the time the warning appeared, the functions that still work, any recent electrical or control work, and photos of the display. Clear observations can shorten the time spent reproducing an intermittent issue.

Gas and carbon monoxide safety

A.02.45 is a connection warning; it is not a carbon monoxide alarm and does not confirm a gas leak. Separate danger signs always take priority. If you smell gas, suspect carbon monoxide, hear a carbon monoxide alarm, see scorching, or notice unusual fumes, stop using the appliance and follow current Gas Safe emergency guidance. Leave the property if necessary and do not investigate inside the boiler.

Quick answers

Does A.02.45 tell me which connection has failed?

No. Baxi describes the warning simply as “Connection error”. The boiler display does not identify one component or cable, so the installed system must be checked.

Is the boiler’s circuit board definitely faulty?

No. The code alone does not prove a circuit-board fault or any other single cause. Testing is required before parts are replaced.

Can I check the wiring?

No. Keep the boiler and connected control enclosures closed. Do not touch terminals, cables, or installer settings. Limit yourself to recording what the normal user-facing controls show.

Will switching the boiler off and on solve it?

A single reset may clear a temporary interruption if the user guide allows it, but a returning warning needs a professional repair. Repeated power cycling is not a fix.