Troubleshoot a Miller oil furnace by checking for common issues, such as tripped circuit breakers, dirty air filters, incorrect thermostat settings and defective flame sensors. Start by examining the simplest options, such tripped circuit breakers, before proceeding to the more complex options.
If a Miller oil furnace does not start, first confirm that the thermostat is on heat and that the setpoint is above room temperature. Reset tripped circuit breakers, and replace any blown fuses. If the problem persists, check to see whether the blower motor or run capacitor is defective, and replace all faulty parts.
If the furnace does not heat, the flame sensor might be defective. A faulty flame sensor does not detect the flame correctly and causes the control board to shut off voltage to the gas valve thereby stopping the ignition process. A flame sensor cannot be repaired and must be replaced. If the problem continues, the air filter may need to be changed or there could an obstruction at the air inlet.
If the furnace is noisy or loud, the blower wheel on the fan motor might be faulty. Check if the screws that attach the blower wheel to the motor shaft have become loose, and if so, tighten them, or replace the blower wheel if it is damaged. If this does not solve the problem, check whether the motor bearings are worn out, and replace them accordingly.