Hi, I am replacing an old T8085a 1004 with a new rth221. There are 4 colored wires from the old thero, colored red, white, green and blue. They were wired Red --> R, White --> W, Green and Blue --> to 2 separate C.
Can someone please advise how they would relate on the new RTH221 thermo. There are 4 openings labeled R, W, Y, and G. I just need to make sure the Y relates to Blue.

Can someone please advise.

TIA

Here is your old thermostat info

http://customer.honeywell.com/techlit/pdf/69-0000s/69-0258.pdf

I need the exact subbase model number. It is under the thermostat. The thermostat fits on to it. I need this to see how it was originally wired.

On the base it states:
191108ba
For 2 wire heat only:
Use r and w terms
For series 20:
Wiring only:
Red to R term,
White to
Unmarked term,
Blue to w term.

I am going to post various subbase diagrams since the exact model number of the one you posted is not available from Honeywell or the number you posted is not accurate.CAUTION these old units had a separate transformer that powered some of the clock circuits. If you hook it up wrong you can destroy your new thermostat. If you do not feel capable of hooking your new thermostat up safetly I suggest you call for a ON SITE service call to sound out the old wiring before a mistake is mead. These change outs can be difficulkt unless you know hot to sound out the old wires and find out exactly where they go on the equipment.

The following subbase circuits are examples of what you have. See if you can find the terminal/wiring layout on one of them.

http://customer.honeywell.com/techlit/pdf/69-0000s/69-0638.pdf


http://customer.honeywell.com/techlit/pdf/60-0000s/60-0771.pdf


http://customer.honeywell.com/techlit/pdf/69-0000s/69-0642.pdf


http://customer.honeywell.com/techlit/pdf/69-0000s/69-0581.pdf

As mentioned before your model number is not listed. I hope one of these will help. This is all the information I have for this subject.

The Diagram is like the one in the second PDF.
Here (http://customer.honeywell.com/techlit/pdf/60-0000s/60-0771.pdf) But I knew how it looks like, Can you tell me how to hook up the wire to the new thermo. The instructions that came with it states I should look for a yellow, green, white and red wires. But I see Blue, Green, White and Red.

First tell me about the unit you are installing this on.

Is it just a furnace?
OR
Is it a furnace with central air?

It is just a gas furance, for heat and hot water. I am currently getting hot water, but no heating.

It is just a gas furance, for heat and hot water.

Gas furnaces do not heat water.

Is this a boiler? What is the brand name and model number that is listed on the unit?

Model is GFS-22 and S/N 21631.
Hey I just want to let you know, I really apperciate your help and patience. I know I am not close to an expert on this matter.

That boiler if about a 1962 model.
I believe you will only use R=RED and W=White for your hookup since you do not have a A/C circuit. Red and White are the heat circuit wire colors used for heat only units.


Here is a electronic copy of your manual see page 1 section 2.3

http://customer.honeywell.com/techlit/pdf/69-0000s/69-2060EFS.pdf

I have the complete tech specs, installation, wiring diagrams, etc, etc for the honeywell thermostat model t8085a,b,c,r & ts8085a cronotherm q 682b,l. e-mail me at [email protected] for the pdf.