18 Low

Baxi 18 Fault Code

The Baxi 18 fault code means: your boiler has switched into a specific mode intended for systems connected to solar panels, which usually happens due to a settings error or a sensor detecting an unusual temperature.. It appears on 3 Baxi 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: Solar plant operating mode
Typical repair cost £0-120 (including labour)

DIY fix possible

Press and hold the Reset button for 5 secondsTurn the power to the boiler off at the fused spur switch, wait 30 seconds, and turn it back onCheck if the boiler has been accidentally put into a solar-only mode via the control panel

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Baxi models that show the 18 fault code

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

Source

Baxi 18 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

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