Ariston
Heating Stuck On (Relay Welded or Wiring Bypass)
Heating runs continuously even when the thermostat is set to OFF or a low temperature.
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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
Welded thermostat relay contacts, Boiler wired permanently on (bypassing thermostat), Zone valve microswitch stuck closed, Incorrect bridging link at boiler terminals
How to Fix / Troubleshooting
Safety: Turn off power to boiler and thermostat before inspection.
- Check boiler terminals: Open the boiler’s wiring compartment and verify that the thermostat terminals are not permanently bridged unless required. Remove any temporary links used during installation.
- Inspect thermostat relay: Disconnect one thermostat control wire at the boiler. Restore power. If heating stops, the thermostat or its relay is likely stuck and should be replaced.
- Check zone valves: For systems with motorized valves, ensure the valve is not manually latched open and that its end-switch is not stuck.
- Replace faulty component: Replace the thermostat or zone valve actuator if they are confirmed stuck on.
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Repair Difficulty
Hard
4/5
Required Part
Ariston Thermostat Relay Output
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