HVACopediaICP · Furnace
10 Line voltage polarity
What the control is telling you
Line voltage polarity is wrong (or furnace not grounded); furnace will not heat. On twinned units also check 24 V transformer phasing.
Applies to: ICP F9MAE / G9MAE modulating variable-speed condensing gas furnaces (060, 080, 100, 120 kBtu/h)
Likely causes
- 115 V hot and neutral reversed
- Missing earth ground
- Twinned units with transformers out of phase
Test and repair steps
- Warning: Turn off power before rewiring.
- Check polarity at the furnace junction box: hot (BLK) and neutral (WHT) correct.
- Confirm a proper earth ground to the furnace and control.
- If twinned, check low-voltage (24 V) transformer phasing.
Models that show this code
6 models in ICP (F/G)9MAE Modulating Furnace
Other codes on the same units
- 5 Abnormal flame-proving signal
- 6 Ignition proving failure
- 6+1 Ignition lockout
- 7 Limit circuit lockout
- 8 Gas heating lockout
- 9 Medium/high pressure switch or PSR relay did not close or reopened
- LED off Amber status LED off - no power / blown 3 A fuse
- LED steady ON Amber LED on solid - control lockout / wrong model plug
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Source: ICP (F/G)9MAE Service and Technical Support Manual 440 04 4700 00, Figure 16 Troubleshooting Chart, p.35. 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.