How to Fix the Baxi E20 Fault Code

The Baxi E20 fault code points to a problem with the boiler's primary temperature sensor (NTC thermistor). This sensor monitors the heat exchanger temperature and helps the boiler control heating safely. When it sends incorrect readings, the boiler enters lockout to protect itself.

The result is usually no heating or hot water until the fault has been diagnosed and repaired.

What Does the Baxi E20 Fault Mean?

The E20 error means the boiler has detected a fault with the primary temperature sensor.

The sensor continually monitors water temperature inside the heat exchanger. If it fails or reports incorrect readings, the boiler stops operating as a safety measure.

An active E20 fault can cause:

• No heating
• No hot water
• Boiler lockout
• A reset that will not clear the underlying problem

If your boiler is showing a different error, see our complete guide to Baxi boiler fault codes for explanations of the most common fault codes.

Common Causes of the Baxi E20 Fault

The most common causes include:

• Faulty NTC thermistor
• Loose or damaged wiring to the sensor
• Faulty PCB (less common)
• Water ingress or electrical damage after a power surge

Most E20 faults are caused by the sensor itself or the wiring connected to it.

How to Diagnose a Baxi E20 Fault

A Gas Safe engineer will usually:

Test the NTC sensor

The thermistor is checked with a multimeter and compared against the manufacturer's resistance values.

Check wiring

Loose, damaged or corroded wiring between the sensor and PCB is inspected and repaired if needed.

Inspect the PCB

If the sensor and wiring are working correctly, the printed circuit board is tested for faults.

Because this involves electrical testing inside the boiler, it should only be carried out by a qualified engineer.

How to Fix a Baxi E20 Fault

The repair depends on the cause.

Replace the faulty thermistor

If the sensor has failed, it is replaced with the correct Baxi part.

Repair damaged wiring

Any damaged or loose connections are repaired before testing the system again.

Test and reset the boiler

Once repairs are complete, the engineer clears the fault code and checks that the boiler heats normally without returning to lockout.

Although you can try a simple reset, repeated E20 errors usually indicate a component fault that needs repairing rather than resetting.

How to Help Prevent Future E20 Faults

Regular servicing helps reduce the risk of sensor-related faults. Good maintenance includes:

• Annual boiler servicing
• Keeping system pressure within the recommended range
• Bleeding radiators when required
• Investigating unusual noises early
• Using inhibitor chemicals and a magnetic filter where appropriate

When to Call a Gas Safe Engineer

If the E20 fault remains after a reset or returns repeatedly, the boiler needs professional diagnosis.

Temperature sensor faults can have several causes, and replacing the wrong part often increases repair costs.

A qualified engineer can identify the fault quickly and safely restore heating and hot water. If your boiler still shows an E20 fault after resetting it, arrange a professional Baxi boiler repair in London before the problem gets worse.

Frequently Asked Questions - (FAQs)

Turn the selector to the reset position and hold it for around five seconds. If the fault returns, further diagnosis is needed.

No. Internal boiler repairs should only be carried out by a Gas Safe registered engineer.

The boiler enters lockout to help prevent damage. However, leaving the fault unresolved may lead to further component failures.

Low pressure is not normally the direct cause, although other heating system faults can sometimes contribute to sensor problems.

Need Help with a Baxi E20 Fault?

If your boiler has locked out or the E20 fault keeps returning, our Gas Safe engineers can diagnose the problem and carry out the repair.

Book your boiler repair today and get your heating and hot water working again.