Trane furnace E6.2: Bad grounding
E6.2 means the furnace does not have an adequate earth ground. Like reversed polarity, it breaks flame sensing while leaving every component in the ignition system testing perfectly.
Applies to: Trane and American Standard S9V2 two-stage condensing variable speed gas furnaces with a seven-segment integrated furnace control display, per Installer's Guide 18-CE01D1-1E-EN.
What it means
The flame rectification circuit returns its signal through the furnace chassis, so the ground is part of the measurement path. A furnace with a poor or missing ground lights normally and reads little or no flame current, and then shuts the gas off. The symptom is identical to a dirty flame sensor, which is why grounding faults get misdiagnosed repeatedly — the sensor gets cleaned, the furnace works for a while as the marginal ground happens to behave, and the fault returns. The Trane flash code system reports grounding as part of a combined code with reversed polarity and igniter faults. Here it has its own code, which is worth more than it sounds.
Most common causes
- A ground conductor not connected, or connected but not bonded to the cabinet.
- A corroded, loose or painted-over bonding point.
- An ungrounded branch circuit, common in older houses with two-wire wiring.
- A ground lifted during earlier service and never restored.
- A ground path through a joint that has degraded with age.
How to diagnose it
- Note whether the furnace has a history of flame sensing complaints or repeated sensor cleanings.
- Note the age of the house wiring — two-wire circuits without a ground are a real cause.
- Check the Last 6 Faults menu for E2.2 or E08 stored alongside this.
- Measurement is technician work; this is not a visual check.
How to fix it
- Provide a proper earth ground to the unit. This is electrician or HVAC technician work.
- Fix this before replacing any flame sensing component, because it is upstream of all of them.
- A ground that is present but poor is still a fault here — adequate is a measurement, not an opinion.
Notes
If a furnace has had its flame sensor cleaned more than once and the fault keeps returning, grounding is the first thing to check and very often the only thing wrong.
Related
All codes for this manufacturer
Trane and American Standard furnace flash codes — every code, with what differs between models.