Schneider Electric
No Power to Thermostat
Thermostat display is completely blank and does not power on.
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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
No 24 VAC supply from HVAC transformer, Loose or broken R/C wires at thermostat backplate, Blown low-voltage fuse on air handler control board, Internal power supply failure in thermostat
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system at the breaker before handling thermostat wiring or opening the air handler.
Steps:
- Remove the thermostat from its wall plate and check that the R (or +24V) and C (common) wires are firmly connected and not corroded or broken.
- Restore power and, using a multimeter if you are trained, measure AC voltage between R and C at the thermostat. You should see approximately 24 VAC.
- If there is no voltage, inspect the air handler or furnace control board for a blown low-voltage fuse (often a 3–5 A automotive-style fuse). Replace only with the same rating and investigate for shorts in thermostat wiring.
- If voltage is present at the thermostat but the display remains blank, the thermostat's internal power supply or display module is likely defective; replace the thermostat.
- Do not attempt to power the thermostat from an external adapter unless explicitly supported by Schneider Electric for your model.
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Repair Difficulty
Medium
3/5
Required Part
Thermostat Main PCB / HVAC 24 VAC Transformer
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