Rheem
No Power to Thermostat
Thermostat display is completely blank and unresponsive; HVAC system does not run.
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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
Blown low-voltage fuse on indoor control board, Failed 24VAC transformer, Broken R or C wire between thermostat and indoor unit, Loose thermostat sub-base connection
How to Fix / Troubleshooting
Safety first: Turn off power to the indoor unit at the breaker before opening panels.
Steps:
- Check indoor unit fuse: Open the blower compartment and locate the 3–5A blade fuse on the Rheem control board. If blown, replace with the same rating after inspecting for shorts in thermostat wiring.
- Verify transformer output: With power on and using a multimeter, measure AC voltage across the transformer's secondary or between R and C on the board. You should see ~24VAC. If 0V, the transformer may be failed and should be replaced by a technician.
- Inspect thermostat wiring: Remove the thermostat and ensure the R and C wires are firmly attached and not broken or corroded.
- Test at thermostat: Measure between R and C at the thermostat sub-base. If 24VAC is present but the thermostat is blank, the thermostat itself is likely defective.
- Replace thermostat if needed: Install a compatible Rheem smart thermostat and follow the installation guide for wiring and configuration.
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Repair Difficulty
Hard
4/5
Required Part
24VAC Control Transformer
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