Ariston
Thermostat Stuck Closed / Control Failure
Water is too hot from an Ariston storage water heater, even at low thermostat settings.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Faulty adjustable thermostat, Welded relay contacts on control board, Miswired heating element bypassing thermostat, Failed temperature sensor reading too low
How to Fix / Troubleshooting
Safety first: Turn off power immediately to prevent scalding and potential tank damage.
- Check thermostat setting: Remove the cover and verify the thermostat dial is not set to maximum. Adjust to 50–60°C.
- Test thermostat: With power off, disconnect one thermostat lead and check continuity. At room temperature, it should be closed; when heated (using a heat gun carefully or hot water on the sensor), it should open. If it remains closed, replace it.
- Inspect wiring: Confirm that the element is wired through the thermostat as per Ariston's diagram. Correct any bypassed connections.
- Replace thermostat or control board: If the mechanical thermostat tests bad, replace it. If a PCB relay is stuck, the entire board must be replaced by a technician.
After repair, verify outlet temperature with a thermometer and adjust as needed.
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Repair Difficulty
Medium
3/5
Required Part
Adjustable Thermostat
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