Furnace grounding and reversed polarity codes
Seven manufacturers publish a code specifically for reversed line voltage polarity or a missing ground, because flame sensing physically cannot work without a good neutral and ground reference.
What the grounding and line polarity does
Flame rectification measures a current of a few microamps flowing from the flame, through the burner and the furnace chassis, back to the control. That circuit is referenced to neutral and to the chassis ground. If line and neutral are swapped at the outlet or in the furnace junction box, or if the chassis is not properly bonded, the control cannot read the flame signal even when the burner is lit perfectly.
Why one part produces several different codes
The result is a furnace that lights and then shuts down a few seconds later, repeatedly, with no fault in any part it names — which is why several brands report grounding and polarity in the same code as an igniter or flame sensing fault. Trane publishes a specific measurement for this: under two volts between line neutral and 24 volt common. Anything higher points at the ground and neutral path rather than at any component.
Every grounding and line polarity code on this site
10 codes across 7 control families. The meaning is the manufacturer's, from the document listed at the foot of each code page.
| Brand | Code | What it reports |
|---|---|---|
| Armstrong | 1 flash | Reverse line voltage polarity |
| Armstrong | 2 flashes | Improper earth ground |
| Carrier | LED rapid flashing | Line voltage polarity reversed |
| Goodman | 8 flashes | Igniter circuit fault, most often caused by poor grounding |
| Goodman | rapid flashing | Reversed 115 volt polarity, a grounding problem, or an open igniter circuit |
| Goodman | E7 | Igniter fault or improper grounding |
| Goodman | EA | Reversed 115 volt polarity |
| Goodman | 9 red flashes | Grounding problem or reversed polarity |
| Trane | 6 flashes | 115 volt AC power reversed, or poor grounding |
| York | 9 red flashes | Grounding, reversed polarity, or reversed transformer leads |
Before you work on it
Confirming polarity and ground means measuring live line voltage. This is electrical work, and in most places correcting reversed polarity at an outlet or panel is licensed work.
Other parts
- Furnace pressure switch codes on every brand
- Furnace high limit switch codes by brand
- Furnace flame sensor codes on every brand
- Furnace rollout switch codes: why it tripped
- Furnace igniter fault codes by manufacturer
- Furnace inducer motor fault codes by brand
- Furnace gas valve fault codes by manufacturer
Sources
Every code meaning above comes from the manufacturer document behind its code page:
- Allied Air Enterprises — A80UH1E and 80G1UHE Installation Instructions 507330-03, Table 7: Diagnostic Codes for -02 Control
- Carrier 58MCB Service Manual, 327884-101 Rev. B — status codes
- Goodman Technical Services Service Bulletin SF-024 — Missing Identification of Eight (8) Flash Fault Code, 3 November 2008
- Goodman Manufacturing — Diagnostic Code Identification System (model-specific fault code lookup)
- Trane Installer's Guide 18-CD29D1-14-EN — Table 21, Integrated Furnace Control Error Flash Codes
- Johnson Controls Unitary Products technical service letter ST-045-09 — York UTEC furnace boards, fault code tables and retrieval procedure