Baxi E.01-.17 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E.01-.17 fault code mean?
The Baxi E.01-.17 fault code signals that the boiler has detected either a problem with water circulation or a fault with one of its NTC temperature sensors. The boiler locks out as a safety measure and will not restart until the root cause is identified and cleared. In plain terms, the boiler cannot confirm that water is moving through the system at the right temperature — either because circulation has broken down, or because the sensor responsible for monitoring it is not giving a reliable reading. This is one of the more frequently seen fault codes on Baxi boilers and covers a range of causes, from a simple loose sensor connection through to a failing circulation pump or sludge-laden system.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or disconnected NTC thermistor Common
The NTC thermistor is a small temperature sensor that tells the boiler's control board how hot the water is. If the thermistor fails, degrades with age, or its wiring connector becomes loose or corroded, the boiler receives no usable temperature signal and triggers E.01-.17. This is the single most common root cause of this code.
- Poor water circulation — airlocks or low pressure Common
If air has become trapped in the system or system pressure has dropped below the minimum threshold (typically around 1 bar), water cannot circulate properly around the heat exchanger. The boiler senses the resulting temperature anomaly and shuts down. Bleeding radiators and checking the pressure gauge are quick first checks.
- Circulation pump failure or seizure Sometimes
The pump is responsible for moving heated water around your heating circuit. A pump that has seized, become partially blocked, or is running too slowly will restrict flow enough to trigger a no-circulation fault. Pumps can seize after a period of inactivity — for example, at the start of the heating season.
- Sludge or limescale build-up Sometimes
Over time, iron oxide sludge and limescale can accumulate inside the heat exchanger and pipework. This restricts water flow and also insulates the NTC thermistor from the water, causing it to report inaccurate temperatures. Systems without a magnetic filter or inhibitor are particularly vulnerable.
- Wiring fault between sensor and PCB Rare
Even if the NTC thermistor itself is fine, damaged, chafed, or intermittently connected wiring between the sensor and the printed circuit board can produce the same erroneous signal. This can be tricky to diagnose without specialist equipment.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Baxi boiler (usually a flame symbol or marked 'Reset'). Hold it for around three seconds, then allow the boiler a couple of minutes to attempt a restart. Do this no more than once or twice — repeated resets without fixing the underlying problem can cause further damage and mask a serious fault.
- Check the system pressure DIY safe
Look at the pressure gauge on the front of the boiler. For most Baxi models it should sit between 1 and 1.5 bar when cold. If it reads below 1 bar, top it up via the filling loop (two small valves on the pipework beneath the boiler) until it reaches approximately 1.2 bar, then close the valves and attempt a reset.
- Bleed the radiators DIY safe
Air trapped in the system prevents proper circulation. Using a radiator bleed key, open each radiator bleed valve until water (not air) dribbles out, then close it again. Start with the radiators farthest from the boiler. After bleeding, re-check and top up system pressure if it has dropped below 1 bar.
- Check the condensate pipe is not frozen DIY safe
In cold weather, the plastic condensate pipe that runs outside can freeze, causing the boiler to lock out. Trace the white plastic pipe to where it exits the property and feel for a frozen section. You can thaw it carefully with warm (not boiling) water or a hot water bottle. Once cleared, reset the boiler.
- Inspect sensor wiring connections (engineer) Gas Safe engineer
A Gas Safe engineer will access the boiler internals to check the NTC thermistor connectors for signs of corrosion, looseness, or heat damage. A poor connection is often the quickest and cheapest fix for this code — the engineer can reseat or replace the connector without necessarily replacing the sensor itself.
- Test and replace the NTC thermistor (engineer) Gas Safe engineer
Using a multimeter, an engineer can measure the resistance of the NTC thermistor and compare it against Baxi's published specification curve. A reading outside the expected range confirms a faulty sensor. Replacement thermistors are low-cost parts and the job is typically straightforward, making this one of the more affordable professional repairs.
- Inspect and service the circulation pump (engineer) Gas Safe engineer
The engineer will check whether the pump is running, measure its output, and look for signs of seizure or blockage. A seized pump can sometimes be freed; a failing one will need replacing. The engineer will also check the pump speed setting is correct for the system.
- Power flush if sludge is found (engineer) Gas Safe engineer
If the engineer finds evidence of heavy sludge or scale — dirty water when bleeding radiators, cold spots at the bottom of radiators, or restricted flow — a power flush may be recommended. This forces a high-velocity cleaning solution through the entire system. A magnetic system filter should be fitted afterwards to prevent recurrence.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the steps above have not resolved the E.01-.17 code, or if the fault returns shortly after resetting, do not continue attempting resets. Contact a Gas Safe registered engineer who can carry out a full diagnostic, test the PCB and all sensors with specialist equipment, and advise whether repair or boiler replacement is the more cost-effective route.
Parts you may need
- NTC thermistor (flow or return sensor) · from £18
- Circulation pump (Grundfos or equivalent) · from £85
- PCB (printed circuit board) · from £180
- Magnetic system filter (e.g. Adey MagnaClean) · from £55
- Central heating inhibitor (1 litre) · from £12
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£380, depending on the underlying cause.
Frequently asked questions
Can I keep resetting my Baxi boiler to clear the E.01-.17 code?
It is fine to try one or two resets after checking pressure and bleeding the radiators, but you should not keep resetting repeatedly. If the fault returns within a short time, repeated resets will not fix the underlying problem and could cause additional wear. At that point you need a Gas Safe engineer to diagnose the root cause properly.
How much does it cost to fix a Baxi E.01-.17 fault in the UK?
Most people pay somewhere between £120 and £380 depending on what is causing the fault. A sensor reconnection or thermistor swap at the lower end, a pump replacement or minor power flush in the middle. If the fault turns out to be a PCB issue — which is less common — costs can rise to £400–£550 including labour, but this is not the typical outcome for E.01-.17.
Could a frozen condensate pipe cause the E.01-.17 code?
Indirectly, yes. A frozen condensate pipe causes the boiler to lock out, and the fault code that appears can vary. However, if your boiler has locked out during or after a cold snap, always check the condensate pipe first as it is a free fix you can do yourself. Thaw it with warm water, reset the boiler, and see if the code clears before calling an engineer.
What is an NTC thermistor and why does it cause this fault?
An NTC (negative temperature coefficient) thermistor is a small electronic sensor that measures water temperature inside your boiler. As temperature rises, its electrical resistance drops in a predictable way, allowing the control board to monitor heating performance. When the thermistor fails, corrodes, or loses its connection, the board receives an unreliable or absent signal and triggers E.01-.17 as a safety lockout. Replacement is usually straightforward and relatively inexpensive for a qualified engineer.