2 Rheem Protech 500 thermostats, 1 upstair & 1 downstairs with a Rudd Achiever 90Plus gas furnace. Thermostat downstairs works fine but upstairs one cycles fan on and off 2-3 times during heating cycle. Have reset thermostat but no change.

Upstairs is usually for winter heating where downstairs is usually for summer cooling.

2-wire heat-only system: Connect one wire to R terminal, one wire to
W terminal


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if there is no control of air movement between floors and you have it on cooling then any cold air will go down to the lower floor
or alternately if you have it set on heating all the hot air will rise to the upper floor
where is the system located (upstairs or down stairs ) and where is the thermostat located
to get control close any upstairs to down stairs doors or erect a heavy curtain across the stair well

Since you have two thermostats that operate the heating unit and the fan, and the fact that neither will turn the blower on, I would suspect the furnace/ air handler. Turn the thermostat to heat and see if the heat and the fan comes on, if it does operate normally in heat, the fan relay or the high speed on the blower is most likely the culprit. (If the furnace is equipped with a circuit board, the fan relay is integral to the board, if it an older furnace it has a separate fan relay). If it does not operate normally in the heating mode, verify power to the furnace, see if the flame comes on, if it does: the fan motor, circuit board or the fan relay are most likely the cause. hope this helps!

check the low voltage on your furnace board.. w terminal to your c terminal.. this will tell you if you are getting signal from your stat.

Take an Amp draw on all heaters and compare. If within 5%, they are working fine but you may have more open area downstairs than up.

Hi, sounds like you determined the problem is not with the thermostat. That leaves the furnace that serves downstairs. What type heating system do you have?

Warm air rises and if the upstairs thermostat is on it will onerride to lower the temp upstairs. To have the dowstairs thermostat govern, the up stairs must be off . The whole house will balance to the controlling thermostat.

Some of this depends on where the air handler/furnace is located. Most often in two story houses, it's in the attic upstairs, or in a closet upstairs. A duct routes air from the furnace to the downstairs supply duct, so it is a distance from the air handler.
When the unit first initiates a heating cycle, that duct is going to be full of cool air, and the duct itself will be cool. So the furnace has to run long enough to push the cool air out, as well as warm the duct up, before your going to feel warm air at the registers downstairs.

Keep in mind, heat rises. And, your thermostat only monitors the immediate area where it's located. In your case, upstairs.
Two story houses are problematic because of this. And one way around it is to have a damper system installed that distributes the air upstairs or downstairs based on a thermostat located in those spaces. There would be 2 dampers, and 2 thermostats (one upstairs, one downstairs). Each stat would control a damper, and the call for heat or cooling.

Let me know if you would like to consider a system like this, and I can point you to components to use. I've put several system like this in.

If you have a volt meter, remove the thermostat off from the mounting plate and check for 24 volts AC across red (R) and White (W). Then check across Red and Yellow (Y). If you do not find any voltage, follow wire as much as you can all the way back to the air handler that is connected to it. Look inside and see if there is a small Auto (car) type of fuse in the wiring harness. Test and replace if necessary. Jump out the Red and Green terminals on the air handler and replace the door. See if the blower turns on. If so, you have narrowed it to the wiring to the thermostat. If not, you have a power problem and will need a technician.