I also have an issue!!!! The PU-5 controller in my unit was damaged and I had to replace it. I did so with the PU-27. The installation was nothing more than removing the old controller and snapping in the new one. I lined up the colored wires with each other and slid the two connection together. (Before making the switch I disconnected the two in-line fuses and replaced them after.) I set up the PU27 to sense the temp at the controller, made the other necessary adjustments, depressed the start button onnce and the heater went through it's normal startup procedure, and the unit came on and all was well. Now when the sensor temp got to three degrees below the set temp the fan started to decrease in speed and the burner slowed down more and more as the sensor temp got closer to the set temp. It slowed down to the point the set temp was never reached. When I increased the sensor temp the heater or fan didn't come back on fully and there never was enough heat to get the place warm. I shut the unit down and let it cool and started over but got the same outcome!! I've done it a number of times and get the same results and I now seem to have an issue where the controller doesn't want to come on without pressing the start bottom a number of times or having to push other buttons first then the start. (Same actions required turning it off). Can anybody help me out?