The Baxi A.00.28 code means the solar temperature sensor is either removed or measures a temperature below range. Those are the two possibilities in Baxi’s current wording. The display does not tell a homeowner which one applies.
This code is relevant only where the installed and configured system expects a solar temperature sensor. It does not mean that every boiler in Baxi’s shared model list has solar equipment, and it does not prove that the sensor itself has failed.
Which Baxi boilers can show A.00.28?
Baxi’s current error-code table lists A.00.28 within a group covering 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.
That model grouping describes where the code can appear, not the equipment fitted in every home. A.00.28 applies in practice only when the controls are configured to expect a solar temperature sensor. Check your system paperwork or ask the installer if you are unsure whether solar thermal equipment is connected.
What is a solar temperature sensor?
In a compatible solar thermal arrangement, temperature sensors provide information that helps the controls manage heat collected by the solar system. A.00.28 says the expected solar sensor is either removed or its reading is below the control’s measuring range.
“Removed” can also describe a connection that the control no longer recognises. “Below range” describes the electrical reading received by the control; it is not the same as saying the weather is cold or there is not enough sunshine.
Does A.00.28 mean my solar panels are not working?
Not necessarily. The code is specifically about the expected solar temperature-sensor signal. It does not by itself assess the performance of a collector, cylinder or the whole solar thermal system.
It is also important not to confuse solar thermal collectors, which help heat water, with solar photovoltaic panels, which generate electricity. If your property has only photovoltaic panels, do not assume A.00.28 refers to them. The system configuration needs to be checked by a professional.
How is A.00.28 different from A.00.29?
- A.00.28: the solar temperature sensor is removed or measuring below range.
- A.00.29: the solar temperature sensor is shorted or measuring above range.
The two codes concern the same broad sensing function but report different signal conditions. Record the complete code so the engineer receives the correct information.
Safe checks you can make
- Write down A.00.28 exactly, including the dots.
- Confirm the full boiler model from the front label or paperwork.
- Check whether your documents mention a solar thermal system or solar cylinder.
- Note whether heating, hot water, or both appear affected.
- Record any other code shown at the same time.
- Tell the engineer about recent solar, cylinder, control or electrical work.
Do not climb onto a roof or open a solar controller, cylinder control, wiring centre or boiler. Do not disconnect the sensor or take resistance, voltage or continuity readings. Do not change configuration settings or installer parameters to make the message disappear.
Can I reset A.00.28?
A code beginning with “A” may be presented differently from a locking fault, depending on the model and circumstances. Do not assume a reset is required simply because the code is visible.
Use only the instructions in the user guide for your exact model. If that guide specifically allows a normal reset for the current condition, one reset is reasonable. If A.00.28 remains or returns, arrange professional attention rather than repeating resets or changing settings.
Could hot water still work?
It may. The effect depends on how the solar thermal equipment, cylinder and boiler are arranged. The boiler or another heat source may still provide some hot water even when the solar sensor message is present.
Do not use apparently normal hot water as proof that the sensor signal can be ignored. Reliable temperature information is part of safe and efficient control of a configured solar thermal system.
When should you seek urgent help?
Arrange prompt help if stored water becomes unexpectedly or dangerously hot, if there is a leak around the cylinder or controls, or if the system repeatedly stops. Keep children and vulnerable people away from unusually hot water.
If you smell gas or a carbon-monoxide alarm sounds, leave the property, avoid switches and flames, and call the National Gas Emergency Service on 0800 111 999 from a safe place.
What should you tell the engineer?
Share the exact code, boiler model, whether solar thermal equipment is installed, what heating and hot water are doing, and whether the message followed recent work. Photographs of the display and accessible equipment labels can help, provided they can be taken without climbing, opening covers or touching components.
For more safe code explanations, visit the boiler help hub.
Is Baxi A.00.28 affecting a configured solar hot-water system?
Book a fixed-price boiler repair aimed at fixing the fault, with the booking price clear before the visit.
Quick answers about Baxi A.00.28
What does Baxi A.00.28 mean?
It means the solar temperature sensor is removed or measuring below range.
Does every listed Baxi boiler have a solar sensor?
No. The code is relevant only where the installed configuration expects that sensor.
Does A.00.28 mean the weather is too cold?
No. “Below range” refers to the sensor signal received by the control, not the outdoor weather.
Is A.00.28 about solar photovoltaic panels?
Not normally. The wording concerns a solar temperature sensor used with compatible solar thermal controls.
Can I test or reconnect the sensor?
No. Do not open controls, disconnect wiring or use a meter. Leave those checks to a qualified professional.