The Baxi 800 System 2 A.00.28 warning means “Solar temperature sensor is either removed or measures a temperature below range.” That complete wording appears in Baxi’s current error-code table for its Combi & System 2 range.
The warning gives two official possibilities: the boiler is not receiving the expected solar temperature-sensor signal, or the value being received is below the accepted range. It does not prove that the sensor itself has failed, and it does not prove that every Baxi 800 System 2 installation has solar equipment.
What does A.00.28 mean?
Some heating and hot-water installations can include additional equipment and sensors. Where a solar temperature sensor is part of the configured system, its reading can help the controls understand the temperature at the relevant point in that arrangement.
A.00.28 means the expected signal is absent or the reported temperature is below the range the control expects. Those are different possibilities. “Removed” can describe an absent signal in the configured system; “below range” describes the value the controls have received. The display does not tell a homeowner which possibility applies.
The warning also does not establish why the signal or reading is wrong. It cannot confirm whether there is a sensor issue, a connection issue, an installation configuration matter or another condition. The correct system information and professional checks are needed before any part is replaced.
Does every Baxi 800 System 2 have solar equipment?
No. The Baxi 800 System 2 is a system boiler that can work with a separate hot-water cylinder. The exact equipment fitted alongside it varies from one property to another. A home may have an ordinary cylinder arrangement, a solar-compatible hot-water system or other controls chosen for that installation.
Do not assume that a roof panel, cylinder or visible pipe is part of a solar thermal system. Check household paperwork for the boiler, cylinder and any renewable-heating equipment. If there are no clear records, give the engineer the full warning and let them identify the installed arrangement.
What might you notice at home?
A.00.28 may appear even when the immediate household effect is limited. Depending on the system configuration, you may notice:
- the warning on the boiler display;
- stored hot water not reheating as expected;
- the boiler running when you expected another heat source to contribute;
- a separate solar or cylinder control showing an alert;
- hot-water availability changing from its normal pattern;
- the warning appearing after controls or heating equipment have been worked on.
These details can help a professional understand the timing, but none of them proves which part is responsible. Record the normal hot-water schedule, what changed and whether the warning is constant or intermittent.
Is A.00.28 the same as a low boiler temperature?
No. The official wording refers to a solar temperature sensor being removed or measuring below range. It is not simply a statement that the boiler, radiators or hot water feel cool. The code concerns an expected sensor signal within the configured controls system.
Likewise, the warning does not prove that outdoor weather has made a collector cold. “Below range” is a technical description of the received reading, not a homeowner instruction to warm, reconnect or adjust anything.
What can you safely check?
Keep the boiler, cylinder controls and any solar equipment closed. You can look at the boiler display, note the full code and check the normal user settings for heating and stored hot water. Confirm whether the cylinder is reheating on its usual schedule and whether other visible controls show a message.
Check household paperwork for the exact cylinder and any solar thermal system. Photographing the outside labels can help when booking a repair, provided they are safely accessible. Do not climb into a loft, onto a roof or into a restricted cupboard to find equipment.
If the exact Baxi 800 System 2 user guide permits a reset, one reset may be tried. If A.00.28 remains or returns, stop resetting and arrange professional help. A reset cannot establish whether the expected signal is absent or below range.
What should you avoid?
Do not touch sensor cables, cylinder thermostats, solar controls or pipework. Do not measure electrical values, disconnect a sensor or alter any installer settings. Keep the boiler casing closed and do not copy configuration values from another installation.
Solar thermal and stored-hot-water equipment can contain very hot fluid and surfaces. Do not handle pipework, valves or collectors, and do not attempt to cool or drain any part of the system. If water from taps is unexpectedly very hot, protect household members from scalding and arrange prompt professional advice.
When should you book a repair?
Professional attention is appropriate when A.00.28 stays on the display, returns after one permitted reset, or coincides with unreliable heating or cylinder reheating. A suitably qualified Gas Safe registered engineer can assess the boiler and its controls. Where solar thermal equipment is fitted, a professional competent in that specific system may also be required.
Seek urgent help if there is leaking hot fluid, steam, smoke, scorching, a gas smell, a carbon-monoxide alarm or electrical equipment exposed to water. Do not approach unsafe equipment simply to read a label or code.
What to tell the engineer
- the full warning code A.00.28;
- the exact boiler model, Baxi 800 System 2;
- whether a separate hot-water cylinder is fitted;
- whether household records mention solar thermal equipment;
- whether heating or stored hot water has changed;
- any message shown on a separate visible control;
- when the warning began and whether recent work preceded it.
This gives the engineer useful context while keeping you away from electrical connections and hot equipment.
Quick Answers
Does A.00.28 mean the solar sensor is broken?
No. Baxi’s wording allows for an absent expected signal or a below-range reading. The code alone does not identify a failed part.
Does the warning prove my home has solar panels?
No. System configurations vary. Check the household paperwork and let a professional confirm what equipment is fitted.
Can I reconnect the sensor?
No. Do not touch sensor connections, wiring, cylinder controls or boiler internals. The system must be assessed using the correct installation information.
Can A.00.28 affect hot water?
It can coincide with changed cylinder reheating or hot-water behaviour where the configured sensor is part of that arrangement. The exact effect depends on the installed system.
Need the boiler repaired?
Your boiler fault is fixed for the agreed price, subject to eligibility and terms.