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Trane E12: Open fuse: the onboard 5 amp fuse is open or missing

Ref. TRANE-E12 · From the Trane furnace manual · Updated 2026-10-23

Status codeE12Trane
What it means

Open fuse: the onboard 5 amp fuse is open or missing.

Call a profurnace
How it shows: 7-segment display alternates with mode: E12

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§1Likely causes

  • Field wiring shorted
  • Unit wiring shorted
  • Accessory drawing more than the fuse rating
  • Fuse not seated

§2Safe DIY steps

  1. Technicianproperly seat or replace the fuse
  2. Technicianmeasure transformer amp draw and correct low voltage wiring
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.

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§4Other Trane codes

E01Trane

Loss of the IRQ or other internal failures (internal furnace control error).

E04Trane

Open limit: main thermal limit, flame rollout switch, or reverse airflow switch.

E05Trane

Flame detected when it should not be present.

E06Trane

Voltage reversed polarity or bad grounding.

E08Trane

Low flame current, but still strong enough to allow operation.

E09Trane

Open inducer limit switch or condensate pressure switch.