I have a1988 Rheem Imperial 90 Plus. When I turn on the heat the furnace exhaust fan comes on, then spark and flame. The fan limit switch rotates and as soon as it reaches low limit and signals the blower fan motor to turn on it trips the main breaker in the fuse box. I removed the fan switch with bracket but was unable to remove the switch from the bracket or the wires from the switch. It looks like the only way to remove the switch is to cut the two red wires since they go to a plug. The two black wires will disconnect; one goes to a snap disk and the other to the pressure switch. I don’t think I will find the direct replacement switch so cutting the wires is not a problem assuming I have diagnosed the problem correctly. Three months ago I replaced the blower fan motor and capacitor. The blower fan motor works with the AC and when switched on manually at the thermostat once the furnace cools down below low limit so I don’t think it is the blower fan motor. How can I test the switch? What else might the problem be? Thank You for any help.

We recently purchased an older home that needs its existing oil-fired boiler to be upgraded (house built in 1965, boiler appears to be the original). The house itself is about 1800sf with two zones of baseboard heat. It appears as though the original boiler had a heating coil for hot water that was later replaced with an electric hot water heater. The burner is vented through a chimney that runs through the center of the house. It has a liner, but we have been told it may not be adequate for propane fired burners and that many newer oil burners will require a new liner with a tighter diameter because of the increased efficiency of newer units. We are at the top of a heavily wooded hill about 45 minutes north of Portland, ME. Living next to a river our hill is generally cooler and very well shaded compared to the surrounding area. Great in the summer, probably an issue in the winter. Natural Gas is not available in my municipality, which leaves us to choose between oil and propane. As noted above, our existing furnace is oil fired. The tank was recently replaced and is in very good shape and complies with the current code requirements. So, no need to upgrade that. I'm not necessarily asking for opinions between propane and oil. I'll call around and try to run the calculations to determine the operating expense savings potential. What I'm more interested in is better understanding the capital expenditures. We've had three separate companies come in and provide evaluations and estimates with respect to replacing our existing boiler with a newer, more efficient model. The first two indicated that we would not be able to reuse our existing chimney (with or without a liner) for a propane fired unit, and would instead need to move the boiler and it's associated piping to the side of the house where we would then have to install new ventilation. Because this would be prohibitively expensive, they felt as though propane wasn't really an option for us. Given that they both said the same thing, we were fairly comfortable with their analysis. However, the third company indicated that a propane fired unit could be ventilated using the existing chimney just fine and that the boiler could be installed in the same location as the existing unit, with the need for expensive piping and ventilation. I've been trying to find information on the ventilation requirements for propane fired units and have to admit I'm either not finding much or not understanding what I am finding. In general, is it possible to use a centrally located chimney to vent a propane fired unit? Also, if natural gas ever becomes available in our municipality, is the same true for LP? A nice situation to be in would be to have the option of easily replacing the burner if something causes a big shift in prices for an extended period of time. Thanks in advance.