[Trainer]

On the A/C electric side of the heater, the inside switch sends a signal to the control thermostat for the burner. If control thermostat is closed, that signal goes on to the relay in the above pic. The relay closes sending A/C power to the two electric elements. If 240 vac is available, both elements heat the coolant. If only 120 vac available, only the 120 vac element heats the coolant.

If relay is OPEN, no electric heat available. So the comment the relay will not close but having electric heating is a real puzzle to me. If I could use my VOM meter, I could diagnose this in a handful of minutes and determine if there is a heater issue or a switch panel issue. If you have a volt meter and can use it, call me and we can diagnose quickly on the phone. 7 one 3 8 one 8 3234

Most burner noise is caused by the plastic clutches. Screaming bearings is certainly possible. One needs to know the normal sound to judge the source of the noise, But most failing bearing slow the rpm down producing poor combustion due to lack of combustion air. The usual result of more fuel than combustion air is black smoke in a diesel burner or engine.

Simple burner service fixes a multitude of burner issues, but not vibrations. So, perhaps the bearings are in need of replacement. It takes about 2 hours to replace the bearings. Snap ring pliers, metric socket head wrenches and high temp grease are needed for bearing replacement.