HVACopediaTrane · Furnace
E12 Control fuse open
What the control is telling you
The 5 A low-voltage fuse on the IFC is blown or not seated.
Applies to: Trane S8V2 (80%, 2-stage, variable speed, Link) and S8B1 / S8X1 / S8X2 (80%, 1- and 2-stage)
Likely causes
- Short in thermostat or accessory wiring
- Accessory drawing too much current
- Fuse loose
Test and repair steps
- Apply power and confirm 24 VAC at TH-TR.
- Check the fuse is fully seated; measure across the fuse terminals - 24 VAC across it means it is open.
- Before replacing, look for shorts in field wiring.
- Run the unit and clamp the transformer red 24 VAC wire: it must be under 5 A.
- Turn on each accessory in turn and measure; correct wiring on any accessory that pushes the draw over the fuse rating.
- If 24 VAC is not present at all, check wiring then replace the IFC.
Settings for these units
Clearance to combustibles · Trane S8V2
| Cabinet width | Vertical sides / top | Horizontal sides / top |
|---|---|---|
| 14.5 in. | 0 / 1 in. | 1 / 2 in. |
| 17.5 in. | 0 / 1 in. | 1 / 2 in. |
| 21.0 in. | 0 / 1 in. | 1 / 3 in. |
| 24.5 in. | 0 / 1 in. | 1 / 5 in. |
24 in. front service access.
3 in. in front of the combustion air openings.
Return filter size by cabinet width · Trane S8V2
| Cabinet width | Filter |
|---|---|
| 14-1/2 in. | 1 - 14 x 25 x 1 in. |
| 17-1/2 in. | 1 - 16 x 25 x 1 in. |
| 21 in. | 1 - 20 x 25 x 1 in. |
| 24-1/2 in. | 1 - 24 x 25 x 1 in. |
Filters are field supplied and mounted outside the cabinet.
Over 1600 CFM upflow: return on both sides, one side plus bottom, or bottom only.
- Return filter size by cabinet width · Trane S8B1, Trane S8X1, Trane S8X2
Models that show this code
37 models in Trane S8V2, Trane S8B1, Trane S8X1, Trane S8X2
Other codes on the same units
- E7.1 1st stage gas valve (MVL) powered with no call
- E7.2 Redundant relay (HLO output) on with no call
- E08 Low flame signal (still running)
- E11 Gas valve relay / valve circuit fault
- E13 Blower motor size / OEM ID mismatch
- E14 Configuration file error
- E17 Blower motor communication error
- E23 Menu data not received by combustion micro (CCM)
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Source: Trane FNR-SVX003A-EN (S8V2 installer's guide) - section Integrated Furnace Control Display Codes, Table 37 Error codes; Trane FNR-SVX003A-EN (S8V2 installer's guide) - section Troubleshooting (flowcharts); Trane 18-CE14D1-1A-EN (S8B1/S8X1/S8X2 installer's guide) - section Integrated Furnace Control Display Codes, Error Codes. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.