Vaillant
Overheating DHW / Temperature Control Fault
Water heater’s hot water is too hot even at low temperature setting
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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 DHW NTC sensor reading too low, Stuck gas valve at high rate, PCB control fault, Incorrectly calibrated temperature knob or sensor
How to Fix / Troubleshooting
Safety: Risk of scalding. Turn the DHW temperature setting down and warn occupants. Isolate power and gas before internal checks.
- Verify setpoint: Confirm the DHW temperature setting on the control panel is not set too high.
- Test DHW NTC: Compare sensor readings to actual outlet temperature. Replace the NTC if it under-reads.
- Check gas valve modulation (engineer): Ensure the gas valve reduces output correctly at low demand. Replace if stuck at high fire.
- Check PCB: If sensors and gas valve are correct, the PCB may be miscontrolling temperature and should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
DHW Temperature NTC Sensor
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