24
Keeprite
Secondary Voltage Fuse Open or 24V Short
Furnace LED shows code 24; thermostat may not control furnace properly.
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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
Shorted thermostat wire, Shorted humidifier or A/C contactor wiring on R or C, Miswired external accessories, Blown 3–5A fuse on control board
How to Fix / Troubleshooting
Safety: Turn off power before replacing fuses or working on low-voltage wiring.
Steps:
- Inspect the low-voltage fuse: Locate the automotive-style fuse on the Keeprite control board. If blown, replace with the same amperage rating.
- Isolate the short: If the new fuse blows immediately, disconnect thermostat wires from the board (R, W, Y, G) and install another fuse. If it holds, reconnect wires one at a time until the fuse blows to identify the faulty circuit.
- Check wiring: Inspect the identified cable run for staples through the wire, melted insulation near the furnace, or exposed copper touching metal.
- Inspect accessories: If a humidifier, air cleaner, or A/C contactor is powered from R and C, disconnect them and test again. Replace any shorted coils or wiring.
Do not upsize the fuse. If the short cannot be located visually, contact a technician for further diagnosis.
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Repair Difficulty
Medium
3/5
Required Part
Low-Voltage Fuse
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