12 FLASH
Tappan
Low 24V Control Voltage / Brownout Condition
LED flashes 12 times; furnace may run but with intermittent issues such as random shutdowns.
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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
Weak furnace transformer, loose low-voltage connections on Tappan control board, short in thermostat cable, overloaded 24V circuit (humidifier, accessories)
How to Fix / Troubleshooting
Safety: Turn off power before checking wiring. Use a multimeter rated for HVAC work.
Steps:
- With power on and furnace idle, measure voltage between R and C on the control board. It should be around 24 VAC. If significantly lower, inspect the transformer and its primary connections.
- Turn off power and tighten all low-voltage screw terminals (R, C, W, Y, G) on the control board and at the thermostat.
- Disconnect any recently added 24V accessories (humidifier, UV light) and see if the problem clears, indicating an overload.
- If the transformer is warm and output is low with no obvious shorts, replace the transformer with a matching VA-rated Tappan-compatible unit.
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Repair Difficulty
Medium
3/5
Required Part
24V Control Transformer
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