TCS STATE (EXTERNAL) Low

Ariston TCS STATE (EXTERNAL) Fault Code

Also written as TCSSTATEEXTERNAL — same fault.

The Ariston TCS STATE (EXTERNAL) fault code means: your boiler is currently on standby because your thermostat is set too low or the boiler is switched to summer mode, meaning it is waiting for a request for heat.. It appears on 1 Ariston 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: There is no demand of heat due to the external regulations of the boiler or boiler is switched on 'summer' position.
Typical repair cost £0-60 (including labour)

DIY fix possible

Check if the boiler is set to 'Summer' mode (hot water only) and switch it to 'Winter' mode if you need heating.Turn up your room thermostat or programmer to ensure it is calling for heat.Check if the batteries in your wireless room thermostat have run out and replace them if necessary.

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Ariston models that show the TCS STATE (EXTERNAL) fault code

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

Source

Ariston TCS STATE (EXTERNAL) fault code information on this page is sourced and cross-checked against the official Ariston service / installation manuals for each affected model.

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