E4
Drayton
Internal Power Supply Fault
Thermostat shows E4 and backlight may flash; device reboots intermittently.
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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 internal voltage regulator, Damaged power supply capacitor, Incorrect supply voltage from receiver backplate, Loose backplate contacts
How to Fix / Troubleshooting
Safety first: Isolate mains power to the heating system and thermostat receiver before removing the thermostat.
- Check supply source: For mains-powered Drayton thermostats (e.g. some Wiser or Digistat models), verify that the receiver backplate is providing the correct voltage as per the installation manual.
- Inspect backplate contacts: Remove the thermostat from the backplate and check for bent, dirty, or corroded spring contacts. Clean gently with a dry cloth and ensure firm contact when refitted.
- Test with known-good supply: If possible, test the thermostat on another known-good Drayton backplate or power source to confirm whether the fault is internal.
- Replace unit if internal fault confirmed: Internal PSU components are not user-serviceable. If E4 persists with a correct supply, replace the thermostat front module or complete thermostat as specified by Drayton.
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Repair Difficulty
Hard
4/5
Required Part
Thermostat Front Module
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