E09
Heatmiser
Low Supply Voltage / Power Fault
Thermostat shows E09 and backlight or display is dim or blank 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
Loose live or neutral at thermostat terminals, Undersized transformer on 12V models, Shared circuit with high-load devices causing voltage drop, Faulty internal power supply on PCB
How to Fix / Troubleshooting
Safety first: Isolate power at the consumer unit or fused spur before removing the thermostat.
Steps:
- Remove the thermostat and check that Live (L) and Neutral (N) are securely connected and not loose or burnt.
- Verify that the supply voltage matches the thermostat rating (e.g., 230V AC for mains models, 12V DC for low-voltage models) using a multimeter.
- Ensure the thermostat is not powered from a circuit that is heavily loaded or switched by another device.
- On 12V systems, check the output of the Heatmiser 12V power supply at the wiring centre or PSU; replace if voltage is low or unstable.
- If supply is correct and connections are sound but E09 persists, the thermostat's internal power supply circuitry is likely faulty and the unit should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Heatmiser Smart Thermostat Main PCB
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