Baxi 600 System 2 E.00.17 fault code: hot-water tank temperature sensor short circuit

If your Baxi 600 System 2 is showing E.00.17, the boiler has detected a problem with the signal from the domestic hot-water tank temperature sensor. Baxi’s current error-code table describes E.00.17 as “DHW tank temperature sensor short-circuited”. DHW means domestic hot water: the stored water that supplies your taps and shower, rather than the water circulating through your radiators.

This is not a code to ignore, but it does not automatically mean the whole boiler or hot-water cylinder needs replacing. It means the control system is receiving an electrical reading it cannot use normally. A qualified engineer needs to establish whether the cause is the sensor, its connection, the associated wiring path, a control issue or something else in the installation.

What does Baxi fault code E.00.17 mean?

On a Baxi 600 System 2, the boiler works with a separate hot-water cylinder. A temperature sensor provides information about the stored water so the system can decide when heat is required and when the target temperature has been reached. E.00.17 indicates that the boiler has recognised a short-circuit condition in that sensor signal.

“Short-circuited” is the manufacturer’s description of the detected signal condition. It is not, by itself, proof that the sensor is the only failed part. A damaged cable, poor connection, moisture at a suitable location, incorrect installation configuration or a control fault can sometimes produce a similar result. The displayed code gives an engineer a useful starting point; it does not safely identify a part for a homeowner to replace.

What might you notice at home?

The exact behaviour depends on how the heating and hot-water system is configured. You may find that the radiators still heat while the stored hot water does not. The cylinder may take longer than usual to recover, the water may remain lukewarm, or hot-water performance may become intermittent. In some installations, the boiler may stop the affected function to avoid relying on an implausible temperature reading.

Do not assume the water is cold simply because a warning is present. If the sensor reading cannot be trusted, treat unexpectedly hot water cautiously, supervise children and vulnerable people, and avoid testing the temperature with your hand under a very hot tap.

Safe checks before arranging a repair

You can collect useful information without opening the boiler, cylinder controls or any electrical enclosure. Write down the full code exactly as shown, including the dots and leading zeros. Note whether the code is constant or intermittent and whether it appeared after a power interruption, maintenance visit or change to the heating controls.

• Check whether the central heating still works normally.
• Check whether hot water is cold, lukewarm, unusually hot or intermittent.
• Look at the normal programmer or room control and note any message shown there.
• Record when the problem began and whether it affects every hot tap.
• Keep the boiler and cylinder casing closed.

If the correct Baxi user guide for your exact appliance permits a user reset, you can try one reset using the stated controls. Do not keep resetting the boiler if E.00.17 returns. Repeated resets do not repair an electrical sensor fault and can erase useful information about when the issue occurs.

What not to do

Do not remove the boiler casing, cylinder thermostat cover or immersion-heater cover. Do not disconnect a sensor, disturb wiring, test resistance or voltage, bridge terminals or attempt to dry electrical components. These tasks can expose live electrical parts, affect safety controls and make the fault harder to assess.

Changing the programmer temperature or repeatedly switching the power off and on is also unlikely to resolve a genuine E.00.17 condition. Leave the system in a safe state and arrange professional attention if normal hot-water service is not restored after the single user-permitted reset.

Does E.00.17 mean the cylinder has failed?

No. The code refers to the temperature-sensor circuit associated with the domestic hot-water tank, not automatically to the cylinder vessel itself. The cylinder can be sound while a sensor or connection needs attention. Equally, replacing a sensor without testing would be guesswork because the detected condition may originate elsewhere in the signal path.

A competent engineer will use the code alongside the system layout, appliance history and measured checks. The repair should address the confirmed cause and then verify that the boiler receives a sensible temperature reading and controls the stored hot water correctly.

When should you book an engineer?

Book a repair when E.00.17 remains after the one reset allowed by the user guide, returns repeatedly, or leaves the home without reliable hot water. Arrange help promptly if the water becomes unexpectedly hot, the cylinder or nearby pipework behaves unusually, or an electrical protective device trips.

This code is about a temperature-sensor signal; it is not itself a carbon-monoxide warning. However, gas smells, suspected fumes or a carbon-monoxide alarm are separate emergencies. Turn off the gas at the emergency control valve if it is safe to do so, ventilate the property, leave the area and follow current Gas Safe emergency advice. Do not wait for a routine fault-code appointment.

What will an engineer check?

The engineer will first confirm the exact Baxi model, code and installation arrangement. They can then assess the cylinder temperature sensor, approved connections and relevant control path using the manufacturer’s service information and suitable instruments. They may also check whether recent work or a control change has affected the way the sensor is configured.

The important point for the homeowner is that E.00.17 needs evidence-led testing, not a parts guess. Once the underlying issue is corrected, the engineer should confirm normal hot-water control and safe operation before leaving the appliance in service.

How to prepare for the visit

Keep a short note of the code, the time it appears and what the heating and hot water were doing. If you know the boiler’s installation date or have service records, make them available. Tell the engineer about recent electrical work, controller changes, cylinder work or power cuts. This information can shorten the investigation without you touching any internal component.

Make sure the boiler, cylinder and controls can be reached safely, but do not remove covers in advance. If there is stored hot water, use it cautiously until the system has been checked.

Quick answers

Can I keep using the heating with E.00.17 showing?

The heating may still operate, but the hot-water temperature signal is not being read normally. Follow the user guide and arrange a repair rather than assuming continued operation is safe for every installation.

Can I fix E.00.17 by resetting the boiler?

A single reset may clear a temporary interruption if the exact Baxi user guide permits it. If the code returns, stop resetting and book an engineer.

Does E.00.17 always mean a new sensor?

No. The sensor is one possible cause, but connections, the wiring path, configuration or controls can also require attention. Testing is needed before parts are changed.

Is this a DIY repair?

No. The checks needed involve electrical components and boiler controls. Keep all casings closed and use a suitably qualified engineer.