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Carrier 24: Secondary voltage (24 V) fuse is open

Ref. CARRIER-24 · From the Carrier furnace manual · Updated 2026-10-23

Status code24Carrier
What it means

Secondary voltage (24 V) fuse is open.

Call a profurnace
How it shows: Status LED: 2 short flash(es) then 4 long flash(es) (code 24)

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§1Likely causes

  • Short circuit in secondary (24 V) wiring, including thermostat leads

§2Safe DIY steps

  1. Techniciandisconnect thermostat leads to isolate the short circuit
  2. Technicianrepair the short and replace the fuse
Safety firstIf you smell gas, do not touch any electrical switch or use a phone in the building; leave immediately and call your gas supplier from outside. Turn off electrical power at the furnace switch or breaker before opening any panel, and never bypass or jumper a limit, rollout or pressure switch. Gas valve, burner, venting, wiring and control-board work should be done by a licensed HVAC technician.

§3When to call a pro

Call a licensed HVAC technician: if the fuse blows again; a short must be located.

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§4Other Carrier codes

13Carrier

Limit circuit lockout: a limit or flame rollout switch was open longer than 3 minutes. Control auto-resets after 3 hours (see code 33).

14Carrier

Ignition lockout: system failed to ignite gas and prove flame in 4 attempts. Control auto-resets after 3 hours (see code 34).

21Carrier

Gas heating lockout. Control will NOT auto-reset.

22Carrier

Abnormal flame-proving signal: flame is proved while the gas valve is de-energized. Inducer runs until the fault is cleared.

23Carrier

Pressure switch did not open.

31Carrier

Low (LPS) or high (HPS) pressure switch did not close or reopened.