Replacing Honeywell thermostat with another Honeywell

flipz

I currently have a Honeywell TH5220D1003 thermostat in my new construction home. I have dual-zone heating and air (one for upstairs and one for downstairs). There are 5 wires hooked up to the downstairs panel in this order:
Red = Rc
(built in jumper from Rc to R)
Yellow = Y
Blue = C
White = W
Green = G

I recently purchased a Honeywell RTH6300B1005. The entire assembly looks exactly the same. The new Honeywell has less pins/connections, however my setup doesn't actually even have wires connected to those extra pins. The new thermostat would fit perfectly on the old assembly and wires matched exactly. The only difference is that on the new one where the Blue (C) wire would go, it's labeled as unused on the wire harness. The old thermostat labels it as "C is optional with batteries".

I wired it up and didn't hook up the blue wire to the new one. I plugged it all in and turned on the circuit breaker and nothing happened. The new thermostat wouldn't turn on. I then plugged the Blue wire in to the spot that says "unused" where it was plugged in to on the old one and still nothing. However I am able to take the old thermostat and put it on the new ones assembly and it turns on perfectly fine. These are both newer thermostats, both are Honeywell, and as I mentioned appear to have the exact same wire harnesses with the exception of some extra unused pins.

Any help would be appreciated. Thanks!

yuri

Check for 24 volts between the R and C on the subbase. With the power On. Yes/No?
Did you put batteries in to the new thermostat and or remove the isolator tab from the end of the batteries (keeps tstat off when in box B4 being sold).

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flipz

So I hate to admit it but I hadn't put batteries in to it (I did that just moments before reading your post). The old one is the exact same design and had a spot for the batteries but there were none in there and it worked fine. But I put batteries in to this one and now everything is working great.

But that leads me to believe it's getting power from the batteries and not from the house. Maybe this model doesn't support being powered from the house?

yuri

Yep. That is why it is unlabelled.

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flipz

Cool, got it. Thanks for the help.