BoilerFaultCodesAriston 7 03 Fault Code
Also written as 703 — same fault.
The Ariston 7 03 fault code means: your boiler is having trouble communicating with one of its internal temperature sensors, which may cause your heating or hot water to work inconsistently.. It appears on 13 Ariston models in our database.
Technical description: Zone 3 outgoing sensor defective
What causes the Ariston 7 03 fault?
This fault occurs when the boiler is unable to read the temperature data from the specific sensor responsible for your third heating zone. The most common cause is a failure of the internal thermistor (NTC sensor) or a loose connection in the wiring harness that links the sensor to the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ariston models that show the 7 03 fault code
Click a model for the full fault code list and model-specific repair notes.
- Challenger 80E Repair: £120-220
- Clas HE 24 Repair: £120-200
- Clas HE 28 Repair: £120-200
- Clas HE 35 Repair: £120-200
- Clas HE Evo Repair: £120-220
- Clas Net One Repair: £120-220
- Clas One Repair: £120-250
- Clas System 28 Repair: £120-200
- E-Combi Evo Repair: £120-220
- E-Combi One Repair: £120-220
- E-Combi One 24 Repair: £90-160
- E-Combi One 30 Repair: £120-220
- Microsystem 15 Repair: £120-220
Source
Ariston 7 03 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