How much does it cost to fix Main error code E20?

Typical repair cost for the Main E20 fault is £90-£160 including labour.

E20 High

Main E20 Fault Code

Q: What does the Main E20 fault code mean?

Your boiler has detected a fault with the internal sensor that monitors the temperature of your central heating water, causing the system to stop working as a safety precaution.

The Main E20 fault code means: your boiler has detected a fault with the internal sensor that monitors the temperature of your central heating water, causing the system to stop working as a safety precaution.. It appears on 5 Main models in our database.

Technical description: Central heating negative thermistor coefficient (NTC) sensor error

What causes the Main E20 fault?

This fault occurs when the boiler's control board loses communication with the temperature sensor or receives an illogical reading that suggests the component has failed. The most common reason is that the internal sensor has suffered an electrical short or has aged to the point where it can no longer accurately track the heat of the water. In some cases, the issue is caused by loose or damaged wiring between the sensor and the main circuit board.

Typical repair cost £90-£160 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Main models that show the E20 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Main E20 fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026