Secondary voltage fuse is open. The chart says to check for a short circuit in the secondary (24 V) wiring.
Bryant 24 on the 80% two-stage chart means the secondary-voltage fuse is open. The only check in that row is a short in the 24 V wiring. It is not code 23, the pressure switch that did not open. The 987MA modulating chart adds thermostat leads to its own code 24. This page does not copy that sentence onto the 80% chart.
Likely causes
- Short circuit in the 24 V secondary wiring
Safe checks for 24
- Count 2 short flashes and 4 long flashes. A new fuse on a shorted wire opens again
- Technicianfind the short in the 24 V wiring, then replace the fuse with the rating printed on the control
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if the fuse is open. Do not install a higher-amp fuse.
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Parts & tools for this fix
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Furnace control board and low-voltage fuse: guide
In this code: Count 2 short flashes and 4 long flashes. A new fuse on a shorted wire opens again
This one is for a technician to test or replace, so we only explain it and do not link to buy it.