F39 Low

ECA F39 Fault Code

The ECA F39 fault code means: your boiler is having trouble communicating with the sensor that measures the temperature outside, which may cause your heating to be less efficient or behave unexpectedly.. It appears on 4 ECA models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Outdoor Temperature Sensor Fault: Outdoor temperature sensor might be defective.
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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ECA models that show the F39 fault code

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

Source

ECA F39 fault code information on this page is sourced and cross-checked against the official ECA service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026