Amazon Smart Thermostat Backlight Degradation or Low Supply Voltage

Thermostat display is very dim but still readable; HVAC works normally

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.

Possible Causes

Aging backlight LEDs, Slightly low 24V transformer output, High load on transformer from additional devices

Safety: Turn off HVAC power at the breaker before measuring voltage.

Measure R–C voltage: With a multimeter, confirm you have around 24 VAC at the thermostat wall plate. If significantly low, the transformer may be undersized or failing.
Reduce load: If multiple accessories (humidifier, zone panel, etc.) share the transformer, consider adding a dedicated transformer.

If voltage is normal and only the display is dim, the backlight is likely aging. Replace the thermostat if readability is an issue.

Medium 3/5

Amazon Smart Thermostat Main Control Assembly

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