Ruud
Intermittent Low Voltage or Internal Power Fault
Thermostat frequently reboots or restarts on its own during normal operation
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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 R or C connection at thermostat, Undersized or failing 24V transformer, Shorting low-voltage wiring when blower or outdoor unit starts, Failing internal power regulator on thermostat PCB
How to Fix / Troubleshooting
Safety: Turn OFF power to the indoor unit before tightening any connections.
- Tighten terminals: At the thermostat and indoor control board, tighten all low-voltage terminal screws, especially R and C. Ensure no bare wire strands are touching adjacent terminals.
- Inspect cable routing: Make sure thermostat wires are not routed across sharp metal edges or moving parts that could intermittently short them when the blower starts.
- Measure voltage under load: With a multimeter, monitor R–C voltage at the thermostat while the system starts heating or cooling. If voltage dips significantly below 22 VAC, the transformer may be undersized or failing.
- Upgrade/replace transformer: If the transformer is overloaded (many accessories on 24V), consider having a technician install a higher VA-rated Ruud-approved transformer.
- Thermostat replacement: If voltage is stable but reboots continue, the thermostat's internal power supply is likely failing. Replace the thermostat.
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Repair Difficulty
Medium
3/5
Required Part
24V Control Transformer (Ruud Indoor Unit)
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