I installed a Honeywell CT87A 4447 thermostat this summer. It worked fine with my air conditioning, but I am having a problem with it controlling my furnace. It will turn the furnace on and I can turn the fan on manually, but when set to auto the fan does not come on.

The thermostat has the following terminal designations: (RH, RC, G, Y, W) and I have the following colored wires: Red, Blue, Green, Yellow, White. I have connected the Red wire to RH, blue to RC, green to green, yellow to yellow, and white to white. In addition, I have jumped RC an RH.

Can you advise if I should change any connections in order to start my fan automatically? :

The blue, if used, should be connected to B or C. With both the red and blue connected to RC, I am surprised you didn't blow a fuse or burn out the transformer. If after you remove the blue wire, the fan still doesn't work, check the limit switch that keeps it from coming on until the furnace heats up.

Seems to have worked

Thanks a million

I have a similar issue with converting from the old round style to a RTHL3550. The difference is instead of a blue wire I have a black wire. I hooked the black wire to the Rc post and used the jumper between rge R and RC. This runs the furnace fine but I have no AC now and the Fan only works in the auto mode. Can you help?

Do you have a red wire coming in at the t-stat and if so what is it hooked up to?

The red wire is attached to the R terminal. I have a black wire that goes to the Rh terminal. I tried swapping these around to no avail.

Gas furnace, heat pump, heat pump with aux heat?

What are each wires color coming out of the wall?

The unit is a gas fired boiler with two zones. One goes to a forced air furnace and the other is baseboard heating, It is the forced air furnace that I am having issues with. Thermostat issues.

The wires are white, yellow, green, red and black.

Thanks.

Rick

I know some Gas furnace guys should be along to get you squared away.

My latitude is too far south in that area.

Send me some names. I am in Medway, MA.

The easiest way is to trace the wires from air handler and get the lables, then match the labels on the stat and wire it up, u also have to set the functions on the stat
If it's a Heatpump with Auxiliary
1-5,2-0,6-9,8-9

Please don't follow the colours as the Honeywell don't follow any standard colour code