Rheem Thermostat problem

______________________________________________________________________ Hello, I had a Rheem Classic 90+ furnace (RGFD) installed in a new house. It is a modulating furnace, so I had a Rheem modulating thermostat installed. The thermostat has malfunctioned (and needed replacement) twice in the last month and a half. The failure does not appear right away, but takes on the order of 1-2 weeks to occur. The thermostat appears to be wired correctly (based on furnace to thermostat wire colors and based on volt meter readings – 24VAC reads as 27.3VAC on the appropriate termainal). The thermostat settings are per the factory, except that a 2 cycle/day setting was selected, rather than a 4 cycle/day. The thermostat has one remote indoor sensor and one remote outdoor sensor, which seem to be providing the correct temperature readings. At thermostat failure, the fan can be activated but the furnace will not generate heat (the R-W connection is not made), even when there is a 10+ degree difference between the actual temp and the set point. Activating the furnace recycle override does nothing. This thermostat has been replaced by a standard mechanical thermostat. The heat works properly (employing the single stage 40-65-100% ramp up cycle over the 15 minute time period) and without failure for weeks. I have contacted Rheem customer service, but they just want to talk to my dealer, so I am trying to find answers in other ways. I should say that the dealer is baffled. Does anyone have any insight into what might be causing the thermostat heat circuit to fail. What can I look for to resolve the problem. Thanks for the help, Phred Replies: fitter597 “Re(1):Rheem Thermostat problem” , posted Mon 14 Nov 19:21 ______________________________________________________________________ Have your contractor install and isolation relay on the heat circuit of the furnace, the new rheem Mods are acting funny when you are only using one averaging sensor with an outdoor air sensor. And if i remember right i think you need to have atleast 3 indoor averaging sensors when you are using them? I could be wrong , check your installation guide the company left you, but to stop the board from wacking your stat, Isolate it with a relay. phred “Re(2):Rheem Thermostat problem” , posted Wed 16 Nov 16:30 ______________________________________________________________________ fitter597, The manual shows 2 indoor sensor hookups: a single sensor and 4 sensors (2 in parallel in series with 2 in parallel). The latter hookup makes the impedance of the single and the 4 sensor cases the same. Do not understand why using 4 sensors would cause it to act any “funnier” than the single sensor case. I will ask about the isolation relay. Phred Freon “Re(1):Rheem Thermostat problem” , posted Mon 14 Nov 15:08 ______________________________________________________________________ Does this thermostat also control AC? See if you can find a wiring diagram to see what other switches are on the R->W circuit. One possibility may be that there may be excessive current through the thermostat due to some other component in that circuit drawing too much. Check the OEM of the thermostat and search on the model number for more information and known issues. phred “Re(2):Rheem Thermostat problem” , posted Wed 16 Nov 16:33 ______________________________________________________________________ Nope, no AC attached. In the mountains, so don’t need one. The heater is the only component on the R-W circuit. Phred