Adc t2000 display, using external 24 v transformer

I have multiple adc t2000 thermostats for a heat only, multiple zone system. Some are powered (wiring: Rh, W, C) from the zone controller; the display on those stays on. Others are powered with an auxiliary 24 v. transformer (wiring: Rh, W from the zone controller and Rc, C from the auxiliary transformer); the display on those does not stay on. Is there a way to keep the display on, for those with the external transformer?

When I installed the thermostats, I gave the wiring on all of them as Rh, W, C as I didn’t want to indicate a system with heating and cooling. Perhaps this was a mistake.

Thermostat has to detect “C” common from same source as your “W” wire for always on display to work.

Since you using zone panel make sure that both wires are coming from that panel to power thermostat.

I have only two wires available from the zone panel, and they have to be Rh and W. Is it documented somewhere that the C wire has to be from the same source as Rh and W?

If I remember correctly there is section about common wire has to be connected to have display always on option working. Also just years of experience dealing with hvac systems.

Your system has to have a common “c” wire coming to your zoning board from your air handler/furnace. If you had previously battery powered thermostat then common “c” wire would not be run to the thermostat.

Post a picture of your zoning board or link to the model of the zoning board. Post pictures of your air handler/furnace control board

Thanks for trying to help. Pictures wouldn’t add any information. For the thermostats in question, I have only a two wire thermostat cable running from the zone controller; no C wire available from the zone controller, and it is too difficult to run new thermostat wire. Baseboard hot water system, no air handler/furnace control board, and no central air. To deal with this situation, I used a secondary 24 v. transformer, removed the Rc-Rh jumper, and wired the secondary transformer to Rc and C.

It may or may not be a design feature/design fault of the particular thermostat that although it is perfectly well powered in this configuration, it still won’t allow continuous display. That was my question.

There are a couple reasons why this might not work. First the system must detect AC power is available. Second, the thermostats must have firmware 1.5+

It looks like two of your thermostats offer the ability to turn the display On and two do not. The setting is found under the user tab in advanced configuration for thermostats in

You can check the version of the tstats while they are in Off mode. While the T2000 mode is off, hold the up arrow button for about 3 seconds. You should see a number displayed (Ex. X.XX) along with the symbols for both heat and cool. This is the firmware version.

The two thermostats that cannot turn on the display are wired differently, as I described earlier. They have firmware versions 2.10 and 1.60.

BTW, one of the other thermostats (labelled “Great room”) behaves differently when I follow your procedure to check the version: instead of displaying the version, it displays “24 v” and then “fossl”.

Unfortunately it sounds like the RC C connection with the jumper removed is likely not being recognized as AC power application when it comes to this setting in ADC. The Display On option can only be applied to thermostats with recognized AC input.

I would bet the Rh input is making that determination. We will forward this to ADC to see if there is any work-around.

Jump the terminals like it originally came out of the box and set up as heat only in advanced tab.

Thank you, Jason, for looking into this.

And thank you adamf for the interesting suggestion. I am wary of either producing a short through the jumper (if the two transformers are out of phase) or an over voltage through the thermostat (if the two transformers are in phase). Perhaps I am wrong about this.

Ok so I think you misunderstood me. There is a jumper on your mounting plate that provides 24V RC and RH. that would be consider your 24V positive power. C is your common wire


You can see jumper clearly mark on the picture

If rc, rh and c gets power from same source your always display on will work.

Yes, thank you. It would be very nice if I could wire everything from one source, but that is not my situation. I necessarily have two transformers involved, so two sources.