EWC-ST-2D troubleshooting / replacement advice

[Climbgunks]

I have a townhouse with a two zone (master/slave) natural gas furnace / air conditioning setup. For the past month or two I've noticed that the furnace tends to short cycle... starts up, but then often only runs for three - five minutes. During really cold days, temperature never gets up to the setpoint on the thermostat (rite-temp programmable -- has worked well for years). The control panel was installed when the unit was built in 2000.

When it short-cycles, there is no indication of a problem on the furnace control board (it has a diagnostic LED).

In trying to diagnose the problem, I first jumpered the RH and W connections at the master thermostat. The unit came on when I restored power to the furnace, but stopped in under 5 minutes as before.

For the second test, I then pulled the R and W wires off the lower left block (goes to the furnace) on the EWC-ST-2D and joined them together. The furnace then started and continued to run while the house came up to temperature (20 minutes or so) and I disconnected the joined wires.

Can I conclude from these two tests that 1) the problem is not with my furnace (due to test 2) and not due to my thermostat (due to test 1)? If so, I'm assuming the issue is with the ST-2D zone controller. My hesitation is because of the dampers -- does the zone controller sense the position of the dampers and if they're not in the correct position, will shut down the signal through R W to the furnace? The LEDs on the damper indicate they appear to be open (I think... one is difficult to see and is going to be even more annoying if I have to replace it).

In the event that I need to replace the zone controller, I would like to have the option of using a wireless thermostat such as a NEST. My understanding is that I'd have to upgrade in that case. Will the NMC-300 be an appropriate replacement that will work with my current setup (master/slave) and with a new smart thermostart in the future? If not, is there a suitable controller for both situations?

Thanks
Todd

[Paul Z.]

Remember the ST-boards only runs from thermostat input. Your test #2 dose show equipment runs with out the board. A NCM-300 will work and then you may use the NEST.