Ok here are all the details. I started with a White-Rodgers Thermostat Type 1F58W-72 and bought a Hunter Set & Save Programmable Thermostat Model 44155C. I took the old one off and labeled all the wires for the new one according to the instruction. It all went well until I realized I had one wire left labeled "X1" and it's a white wire. Loooking around on line it made me think that I have a "multi-stage heat pump" and this new thermostat only takes single stage heat pumps. I went to Lowe's and purchased the Honeywell RTH7000 which is supposed to work for them. Still I have no idea where the "X1" wire is supposed to go.

Currently, I have the following wires labeled and hanging outside of the wall:

1. "G" Greeen
2. "RH" Red
3. "W/B" Blue
4. "Y/O" Yellow

These are the labels from the Hunter but they seem to match what the Honeywell needs. What I need to know is where will the "X1" go please? Looking at the earlier mentioned wires, where will I put them on the Honeywell; just to make sure I do not screw it up? The wires on the Honeywell can go into the "Conventional" area: C, G, Y, W, RC, R, W2, Y2 or the "Heat Pump" area: C, G, Y, O/B, RC, R, AUX, E, L.

Apologies for the lengthy post but wanted to include all data. Thanks in advance for any help. Also, our home has central heating/cooling if that is any help. HAppy New Year!

Look under the sticky notes at the beginning of this board for thermostat color/number/letter combination codes.

1st of all RTH7000 is a series. Need better numbers.

Let's determine if you have a HP or conventional T-stat. If your outside unit runs when your calling for heat and it's 50 deg. Outside you have a HP. Did it have a mode called "Em heat" or "Aux heat"? This would indicate a HP.

X1 might be a conventional terminal or a HP terminal.

Were you replacing a mechanical stat? Was it digital? Battery powered?

HVAC1000:
X1 isn't in the sticky. Could be Common. Could be reversing relay.

yep X1 is missing from the sticky.

skdpat you might look at the doc below. It covers the 7000 series stat. 7400 and 7500.

http://customer.honeywell.com/techli.../69-1900EF.pdf


Page 10,11, and 12 offer wiring options and other info.

Good luck.

Thanks for the prompt responses. First off, its an RTH7400; was not aware it was a series. The old thermo that I am replacing is mechanical (mercury inside); it does an "Aux heat" and "Emer heat" (both) on the outside. When I looked up the original thermo, it stated it was a multi-stage heat pump thermostat... dont know what that means for certain. Thanks for any additional help

That's not going to be the issue. What's going to be the problem is the lack of a "C" terminal. "C" has been created to deal with Electronic Programmable Thermostats. It esscence allows the thermostat to receive constant power from the furnace. "Power stealing" and "Battery powered", not to be confused with "Battery backup" are ways of dealing with the lack of a "C" terminal. There is another method, probably best left for professionals that can avoid running more wires or a larger cable.

You could still have either especially with the dual markings you listed.

A mechanical stat with X1 suggests a Heat pump w/o aux. heat.

With a Heatpump the outside unit runs for both heating and cooling. With conventional, the outside only runs in cooling. Figure that one out or find the paperwork.

Do you have any extra unused wires available in the thermostat cable?

Go to your air handler and identify which wires connect to which terminals. Unlike furnace-A/C systems which mostly use the same 4-5 wires, heat pumps have more wires for more functions and don't always use the same labels. You need at least a connection diagram for your system to mesh it with the thermostat. Also, if you could dig up the instructions for the WR thermostat, perhaps on line, it should tell what the X1 was doing. Likely it activates one of the stages of heat.

''Also, our home has central heating/cooling if that is any help. '' Does that mean you also have a furnace? Did you use the sticky to verify that you indeed do have a heat pump? If you can't find any directions for your system, post the brand and model and maybe somebody can find them for you.

Never apologize for giving too many details. The people that need to apologize are the ones giving too few. As you can see, we have had to ask for even more.

There is one t-stat from the Honeywell Vision Pro line that only requires 3 wires because it "communicates" to a "relay" box mounted in the furnace. More info here:

YTH9421C1002: $199.00 | Honeywell VisionPro IAQ Programmable MultiStage Thermostat with Total Home Comfort Control | iaqsource.com - Aprilaire, Honeywell, Trion Air Bear, Bryant, Carrier, Trane Filters and IAQ products