H3
Ideal
Return Thermistor / Temperature Sensor Fault
Ideal boiler shows H3, hot water temperature unstable or boiler cycles rapidly
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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 return NTC thermistor, Loose or corroded connector, Damaged harness, PCB sensor input fault
How to Fix / Troubleshooting
Safety first: Allow the boiler to cool before any work. Internal access must be by a Gas Safe engineer.
User steps:
- Reset once: Turn the boiler off and on, then reset.
If H3 persists, an engineer should test and replace the return NTC thermistor and check wiring and PCB.
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Repair Difficulty
Hard
4/5
Required Part
Return NTC Thermistor
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