Nest Thermostat and 15V Heat

Keither

I have central air / heat (gas) and installed a Nest thermostat during the summer which has been working great. I just realized the other day when switching over to heat that it wouldn't turn my heat on. After doing quite a bit of troubleshooting I found out that while my cooling and common wires are all 28VAC, the heating wire (white) is only 15V and since the nest requires 24V it won't turn the heat on. Nest customer service said it's unusual for every lead to be 28V while the heating is only 15 and suggested it might be a transformer issue... Based on that, my maintenance guy swapped out my transformer.. but the white wire is still only 15V..



So I'm wondering.. 1. Is this normal?  and 2. Can I rig something up like a 24v transformer and a relay to get around this?



The odd thing is the marking on the old transformer and relays they swapped out all say 24VAC on them.. so I'm surprised I'm getting 15v...

-Keith



-Keith

Techman

Nest

What type of heat appliance do you have? Furnace? Boiler? What is the VA rating of the xformer?Remove the white wire @ the heat appliance and measure the voltage.If you have your 28v then touch the white wire back to where you disconnected from with the volt meter still attached ,if the volt drops then the problem is probably somewhere in the heater All of that stuff is refered to as 24v,xformer,relays,gas valve,ect.the actual voltage is then compared to the "normal" 24v. The t'stat doesn't use the voltage (mostly) it is just a couple of switches,KindaSorta like your wall light switch.Is there another xformer in the heating appliance?