Lennox SL280UH090V60C-05
Damper Control Module 103916-01
S30 Smart Wi-Fi t-stat in main room
17A30 zone t-stat in bedroom zone.
Outside Lennox AC.
Installed 2019.
We have two such setups in the house, one system works fine but the other started getting error E124 when using zone heat this fall.
The system that works well has DCM HW/SW 003/001.
The system that throws E124 has DCM HW 002/001. Not sure if previous owner replaced one DCM.
We can heat the main room if not also calling for heat in the bedroom zone.
Get error E124 when calling for heat in the bedroom with or without calling to heat the main room.
E124 is no comms for 3 minutes from t-stat.
When I swap the 17A30's between the two systems the problem stays with the bedroom, so all t-stats are good.
Dampers seems to be actuating properly.
12VDC looks good.
Resistance of comms bus loop is about 3 Ohms (two middle wires disconnected from t-stat and DCM, joined at one end, measured at the other end).
Same for bus loop from DCM to furnace controller. Now, I know that cheap meter reads too high compared to my good one but that's what I had up in the attic so not sure what to make of the wire resistance.
The t-stat wiring doesn't appear to be shielded and the extra wires are unterminated. Been that way since the beginning but the E124 problem just started.
Any ideas what to try next?
Seems to point to the the DCM. Does a new unit require a service tech to program?
Thanks for any feedback!