The Baxi 600 System 2 A.00.29 warning means “Solar temperature sensor is either shorted or measures a temperature above range.” That is the full wording in Baxi’s current error-code table for its Combi & System 2 boilers.
The wording contains two separate possibilities: the control is receiving a signal consistent with a short circuit, or the reported solar temperature is above the accepted measuring range. The display does not tell a homeowner which possibility applies. It also does not prove that the sensor needs replacing or that a solar circuit is physically overheating.
What does A.00.29 mean?
Some heating and hot-water systems include additional temperature sensors. Where a solar temperature sensor is fitted and configured, its information can be used by the controls to understand conditions in that part of the installation.
A.00.29 indicates that the expected sensor information is not within the normal form or range. “Shorted” describes the electrical character of the signal the control has detected. “Above range” describes a measurement beyond the range expected by the system. These are not the same thing, and neither can be confirmed by looking at the display alone.
A competent professional needs the correct model information and details of the installed hot-water and solar equipment before checking the system. The code should not be used to guess a failed component or order a replacement sensor.
Does every Baxi 600 System 2 have solar thermal equipment?
No. The Baxi 600 System 2 is a system boiler designed to work with a separate hot-water cylinder, but household installations vary. Some may include solar thermal equipment and related controls; others may use a conventional cylinder arrangement without it.
The warning can relate to how the system is configured as well as to equipment that is physically present. Do not assume that roof panels, a cylinder or unfamiliar pipework are solar thermal components. Check any safely accessible household records for the boiler, cylinder and renewable-heating equipment, then give those details to the engineer.
What might you notice at home?
A.00.29 can appear with different household effects. You may notice:
- the warning on the boiler display;
- stored hot water not following its normal reheating schedule;
- a separate cylinder or solar controller showing an alert;
- hot water being warmer or cooler than expected;
- the boiler running at an unusual time to reheat the cylinder;
- the warning appearing after work on heating or hot-water controls.
These observations help establish the timing but do not identify the cause. Record what changed, whether central heating is affected and whether the warning is constant or intermittent.
Does “above range” mean the system is overheating?
Not necessarily. “Above range” is part of the official fault description for the sensor reading. It does not, by itself, prove that the water, cylinder, collector or solar fluid is dangerously hot. A signal fault and a genuine high reading can look different to a professional, but the display does not make that distinction for the homeowner.
Treat actual signs of excessive heat separately. If tap water is unexpectedly scalding, keep vulnerable people away from it and arrange prompt professional help. If there is steam, leaking hot fluid or unusually hot accessible surfaces, do not approach or touch the equipment.
What can you safely check?
Keep the boiler, cylinder controls and any solar equipment closed. You can read the full code, check the normal user settings for heating and hot water, and note whether the cylinder reheats on schedule. Look only at visible control displays and safely accessible labels.
If paperwork identifies a separate solar controller, record any message shown on its normal display. Do not press installer buttons or change configuration values. Photographing an accessible outside label can help when booking, but do not climb into a loft, onto a roof or into a confined area.
If the exact Baxi 600 System 2 user guide permits a reset, one reset can be tried. If A.00.29 stays on the display or returns, stop resetting and arrange professional attention. A reset cannot determine whether the signal is shorted or the measured value is above range.
What should you not do?
Do not disconnect or reconnect a sensor, inspect terminals or test electrical values. Do not remove the boiler case, cylinder covers or a solar controller cover. Avoid any online instruction that asks you to measure resistance, continuity or voltage, change installer parameters or copy settings from another property.
Do not touch solar pipes, collectors, valves or cylinder connections. Solar thermal systems can contain very hot fluid even when the boiler is not firing. Any work on that equipment belongs to a suitably competent professional.
When is professional repair needed?
Book a repair when A.00.29 remains, returns after one permitted reset or coincides with unreliable heating or stored hot water. A Gas Safe registered engineer can assess the boiler and its controls. If solar thermal equipment is fitted, a specialist competent in that installation may also be needed.
Seek urgent help if there is steam, leaking hot fluid, smoke, scorching, a burning smell, water affecting electrical equipment, a gas smell or a carbon-monoxide alarm. The code itself is not a carbon-monoxide reading, but an independent alarm or safety sign must take priority.
What to tell the engineer
- the full warning code A.00.29;
- the exact boiler model, Baxi 600 System 2;
- whether a separate hot-water cylinder is fitted;
- whether household records mention solar thermal equipment;
- any message on a separate visible controller;
- whether heating or hot-water behaviour changed;
- whether the warning followed recent work;
- whether one user-guide reset changed anything.
This information gives the engineer useful context while keeping you away from hot equipment and electrical connections.
Quick Answers
Does A.00.29 prove the solar sensor is faulty?
No. Baxi’s meaning covers a shorted signal or an above-range reading. The display alone does not identify a failed part.
Does the code mean the solar circuit is overheating?
Not by itself. “Above range” describes the sensor reading seen by the controls. Actual signs of excessive heat should be treated separately and urgently.
Can I test the sensor myself?
No. Keep all covers closed and do not touch wiring, sensor connections, hot pipework or installer settings.
Can A.00.29 affect hot water?
It can coincide with changed cylinder-reheating or hot-water behaviour where the configured sensor forms part of that system.
Need the boiler repaired?
Your boiler fault is fixed for the agreed price, subject to eligibility and terms.