Lennox furnace doesn't work after changing out thermostat to an Aprilaire model 8870 communicating thermostat. Have triple checked the most obvious and wiring at both ends. Furnace powers up but will not ignite. Have changed out the new Aprilaire for another exact model. Still no luck! Thermostat works okay shows status etc. but will not even manually turn furnace on. Nor does the FAN turn on even manually. This Lennox has a "SureLight" motherboard in it. Any ideas? :confused:

Put your old thermostat back on and see if that fixes it. If it does leave it alone and enjoy the heat.

But that ultimately defeats the purpose! I did exactly that before packing up because I had to restore 'heat' to that zone of the church for Sunday services.

More specifically, this is only one of three Lennox HE furnaces to remote control via Automation. The church has an Elk M1 Gold Alarm System/Home Automation System communicating via RS232 to a Protocol Translator via RS485. The three Aprilaire Thermostats are pig-tailed at the Protocol Translator [also Aprilaire!], then CAT5 wired to the wall mounted Aprilaire 8870 thermostat, then your typical 5 wire [R,C,G,W1,W2] from the thermostat to the furnace's mainboard. The Aprilaire thermostat is network addressable from the PT. I can communicate two-way from the Thermostat. But it will not control the furnace as does the Honeywell.

The Elk M1 Gold is compatible with Aprilaire products and is the reason for using them. I am due to contact Aprilaire this morning and ask, but on Saturday I thought I might get a more quick answer online!

Dave

It is always better to go back to the factory for an answer when you are dealing with problems especially problems of this type. Many times the factory will not have the answer but they can look into there data base of problems and help you alomg the way. My experience with electronic control is limited to the three zone system in this house which is controlled from the main frame of the server with area sensors. Each brand of equiptment has its own querks. Sorry I could not be of assistance but at least you have the heat back on and that is what counts in this weather.

Found the problem... corrected it, whalla! It works fine now!
I needed to jumper the "R" and "C" terminals over to the "RH" and "RC" terminals to provide 24v power to the thermostat.
Dave
P.S. thanks for the help though!

You jumpered the C into what terninal?

You jumpered the C into what terninal?

I caught that but he seems to think it works. LOL

I connected the "R" red from furnace to the Aprilaire's "RH" then jumpered the "RH" over to the "RC" then jumpered the "RC" over to the Aprilaire's "R" terminal. The "C" from the furnace goes direct to the "C" terminal of the Aprilaire thermostat.

Hope that clarifies what I've done... anyway, seems to function properly now and communicates with the Elk M1 Gold automation system components. Aparantly, this is the way for a TWO STAGE w/AC. But no Heat Pump here, so no connections to Y1 or Y2.

Dave

p.s. I had some zoning in a house, the new thermostat had also be wired this way, even though the old one did not. Honeywell zoning