Baxi E40 Fault Code: What It Means & How to Fix the Error Safely
The Baxi E40 Fault Code is triggered when there’s an issue with the central heating return NTC sensor, a key component that monitors the temperature of water returning from your radiators. If this sensor fails or gives inaccurate readings, your boiler may not heat properly or could shut down for safety. This guide explains what the Baxi E40 Error Code means, what causes it, and how a professional can safely fix it.
Table of contents
What Does the Baxi E40 Fault Code Mean?
If your Baxi boiler shows the E40 error code, it’s telling you there’s a problem with the NTC thermistor on the return heating flow. This small sensor checks how hot the water is when it returns from your radiators.
Without accurate temperature readings, the boiler can’t work efficiently. It’s like cooking without knowing the temperature of your oven – your heating may underperform or shut off altogether.
Common Causes of the Baxi E40 Error Code
The E40 fault is most often caused by:
- Loose or faulty wiring to the return temperature sensor
- A faulty or damaged NTC thermistor
- Disconnected or improperly connected sensor wiring
These sensor-related issues are typically minor but require professional diagnostics to fix properly. Ignoring them may lead to boiler shutdowns or poor heating performance.
How to Fix the Baxi E40 Fault Code
Time needed: 5 minutes
Fixing the E40 fault on a Baxi boiler involves the following steps:
- Inspect the Sensor Wiring
A heating engineer will first check all wiring to the return thermistor. Many faults are caused by simple connection issues.
- Test the Thermistor
Using a multimeter, the engineer will check whether the thermistor gives the correct resistance values. If not, it will need replacing.
- Replace the Sensor if Needed
If the thermistor is faulty, it will be swapped with a compatible part designed for your Baxi boiler model.
When to Call a Gas Safety Engineer
If you see the Baxi E40 Fault Code, it’s best to avoid DIY repairs unless you’re trained. A certified Gas Safe engineer can:
- Safely test and replace the sensor
- Check for hidden issues like internal wiring faults
- Ensure your boiler is reset and working efficiently after the fix
Final Thoughts
The Baxi E40 Error Code is a common boiler fault related to your central heating return sensor. While the issue may seem technical, it’s usually an easy fix for a qualified heating engineer. By addressing the problem quickly, you can get your boiler back to delivering warm, reliable heating without disruption.
Frequently Asked Questions
The process of resetting your boiler is the same regardless of the fascia display. To reset the boiler, turn the selector switch to the R (Reset) position. Hold for at least 5 seconds and release. The fault code will be replaced with the boiler’s current temperature.
If your boiler has power and your boiler pressure is 1-2 (normal boiler pressure) or in the green range on the dial, then you’re safe to try a boiler reset.
An E118 fault on your Baxi boiler means the water pressure is too low. The system can’t operate correctly. The first step is to check the pressure gauge on your boiler. If it reads below 1 bar, you need to repressurise the system.
