High
floor thermostat contact open on Ariston Clas One

Your boiler has automatically shut down because the water inside the system has become dangerously hot.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

If the outlet temperature is too high, the boiler will stop both domestic hot water and the heating production. Flashing light (Green Leds Temperature indicador 40 and 70) will restart when the thermostat is closed during automatic resetting.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related fault codes

1 01View →1 02View →1 03View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →