Baxi 600 System 2 A.02.36 warning: functional device disconnected

The Baxi 600 System 2 A.02.36 warning means “Functional device disconnected.” That is the exact wording in Baxi’s current error-code table for its Combi & System 2 boilers.

The warning tells you that the boiler’s controls are no longer detecting a device expected by the configured system. It does not identify the device. It also does not prove that a thermostat, sensor, accessory, cable or boiler control has failed.

What does A.02.36 mean?

Modern heating systems can include controls and accessories that exchange information with the boiler. Which devices are present depends on how the individual property was designed and configured. A.02.36 records that a device treated as functional by that configuration is disconnected or no longer detected.

The display cannot tell the homeowner whether the device has been physically removed, has lost communication, is incorrectly configured or is affected by another problem. “Disconnected” describes what the control system has detected; it is not an instruction to reconnect a visible wire or pair a control.

A competent engineer needs to establish what equipment is actually fitted, how it was configured and what changed before the warning appeared. That assessment should happen before any part is ordered or replaced.

What might you notice at home?

The Baxi 600 System 2 normally provides central heating and reheats a separate hot-water cylinder. Depending on the missing device and the system design, you may notice:

• A.02.36 on the boiler display;
• heating not following the room temperature setting;
• the cylinder not reheating on its usual schedule;
• a visible thermostat or programmer appearing offline;
• one heating zone not responding while another still works;
• the warning appearing after controls or heating equipment were changed;
• the boiler continuing to run but with reduced control.

None of these observations identifies the disconnected device. Record which service is affected, what the visible controls show and whether the warning is constant or intermittent.

Does A.02.36 name the failed device?

No. Baxi’s wording is deliberately general: “Functional device disconnected.” The code does not name a thermostat, sensor, receiver, cylinder control, accessory or internal component. A device visible in the home may be unrelated to the warning.

Do not replace the first control that appears unresponsive. A control can look offline because of the wider system condition, and an engineer may need to review the configured equipment before deciding what requires attention.

How is this different from similar Baxi codes?

Baxi lists A.02.37 separately as “Passive functional device disconnected” and E.02.35 separately as “Critical safety device disconnected.” Those are different official descriptions. A.02.36 should not be merged with them or treated as proof that a critical safety device is involved.

Always report the complete code, including every dot and digit. Similar-looking codes can lead to different checks, so the exact display matters more than a general description such as “device fault.”

Is A.02.36 specific to the Baxi 600 System 2?

Baxi includes the Baxi 600 System 2 in the current Combi & System 2 group that lists A.02.36. Fault-code meanings can differ between ranges. Confirm the full model name on the appliance case or household paperwork before relying on this meaning.

If the appliance is an older Baxi 600 System rather than a Baxi 600 System 2, use the documentation for that exact model. Give the model and complete code to the repair provider.

What can you safely check?

Keep the boiler and all controls closed. You can check the normal user settings on visible thermostats and programmers, note whether their displays are lit and record any ordinary status message. If a visible control uses homeowner-replaceable batteries, follow only that control’s own user instructions.

Check whether heating, stored-hot-water reheating or a particular zone has stopped responding. Note whether the warning began after a service, thermostat replacement, building work, power interruption or change to a heating schedule.

If the exact Baxi 600 System 2 user guide permits a reset, one reset can be tried. If A.02.36 remains or returns, stop resetting and arrange professional help. Do not use a reset loop to keep the system operating.

What should you not do?

Do not open the boiler, receiver, thermostat or wiring centre. Do not bridge terminals, swap wires, change polarity, measure electrical values or copy a pairing sequence from another system. Do not enter installer menus or alter configuration settings.

Different homes can use different controls with the same boiler model. An online instruction for a similar-looking installation may not match yours and can create additional faults or safety concerns.

When should you arrange a repair?

Book professional attention if A.02.36 stays on the display, returns after one permitted reset or prevents heating or cylinder reheating from working normally. A suitably qualified Gas Safe registered engineer can assess the boiler and determine whether another controls or electrical specialist is also required.

Stop using the appliance and seek urgent help for any separate gas smell, carbon-monoxide alarm, smoke, scorching, sparking, burning smell or water entering electrical equipment. A.02.36 does not itself identify a gas or carbon-monoxide event, but an independent safety warning always takes priority.

What to tell the engineer

• the full warning code A.02.36;
• the exact model, Baxi 600 System 2;
• whether heating, cylinder reheating or one zone is affected;
• what each visible thermostat or programmer displays;
• whether recent controls or heating work took place;
• whether there was a power interruption;
• whether the warning is constant or intermittent;
• whether one user-guide reset changed anything.

This provides useful context without asking you to inspect wiring or identify the device yourself.

Quick Answers

Does A.02.36 mean my thermostat is broken?

No. The code does not identify the disconnected device or prove that a thermostat has failed.

Can I reconnect the device?

No. Keep covers closed and do not touch wiring, terminals or installer settings. The installed configuration must be checked professionally.

Is A.02.36 a critical safety-device code?

No. Baxi lists a different code and wording for a critical safety device. Report A.02.36 exactly as shown.

Can the warning affect hot water?

It can affect cylinder reheating if the disconnected device is relevant to that part of the configured system, but the code alone does not identify it.