1% Low

Heatline 1% Fault Code

Also written as 1 — same fault.

The Heatline 1% fault code means: your boiler is struggling to detect the outside temperature, so it may not be adjusting its heating levels as efficiently as usual.. It appears on 1 Heatline model 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: Fault on Outdoor sensor
Typical repair cost £120-180 (including labour)

Engineer required

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

Find a Gas Safe engineer

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Heatline models that show the 1% fault code

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

Source

Heatline 1% fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.

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