We recently replaced an old thermostat with a programmable thermostat, and now the heat won't kick on. My husband said he switched the wires directly over, and the AC works fine. But when we switch to heat we can hear the unit turn on, but the fan doesn't turn on or blow out anything. This is a manufactured home, built 9 years ago. The wires coming from the wall are red, white, yellow and green. The thermostat has 5 connections, Rh, Rc, W, Y, G, with the Rh and Rc connected by a jumper. They're currently connected by color, and again, the AC works, but we have no heat. Any thoughts?

Red should be common power, white is heat, yellow is cool, and Green is fan.

Use this setting if you have a gas or fuel oil furnace.
In this setting, when the fan is placed in
automatic mode, it works as follows:
• When the thermostat is placed in cool mode,
the fan works only when cooling is activated.
• When the thermostat is placed in heat mode,
the fan is controlled by the furnace fan control
circuitry.

I'm wondering if this could have something to do with the fan not coming on when the thermostat is turned to heat. Is it possible that the thermostat isn't compatible with our system?

Down here in Florida we don't have Heat only, or Gas that I Know of.
99.9% of systems down here are Inside Air handler, and an outside Compressor Unit.
The outside Compressor Unit gets 24 volts from Blue or yellow of Thermostat Connection and transformer, when cooling, there is also power to Blower motor Relay/Contactor.
In Heat, thermostat connects Red/power(R) to White/heat(W), and also to Green/Fan(G) for blower motor. The Blower, Compressor, and Heat Strip will use a 24 Volt(Usually)Relay/Contactor for Control.
Hope something here helps.

Called Honeywell, and they said that the t-stat is calling for heat, but that the furnace, for some reason or other, isn't telling the fan (blower) to turn on. Tips for troubleshooting?

It is likely the white wire from the thermostat goes to a Relay/Contactor in Air Handler? need to see 24 volts at heat strip contactor when set to heat, If it is a contactor, you may be able to manually override and see if Heat responds. If you have 240 volts out of heat contactor and no heat, element is open, or wiring.

Okay, I'm sorry, but I only understood about half of what you said.:confused: Are you saying that it's possible that the white wire isn't connected well enough or that it might not be getting power from the furnace? I need to check with a voltage tester? (sorry I don't know the name!)

We got it figured out... first we found that the burners weren't lighting. Fixed that, but the t-stat still didn't turn the fan for the furnace on. Changed the t-stat again, and now everything's working. Thanks!

Great!