The flames on the gas burner should be full and steady, with no sputtering and no trace of yellow. To adjust the flame height on the main burners, call a professional service person. To adjust the height of the pilot flame, turn the flame adjustment screw until the flame is from 1 1/2 to 2 inches (3.8 to 5.1 centimeters) high. The adjustment screw is located near the gas valve on the pilot assembly, if the control has this adjustment feature.
If you suspect leaks around the furnace unit, stir up a mixture of liquid detergent and water. Paint this mixture on the gas supply line along its connections and valves; the soapy water will bubble at any point where there's a leak. If you find a leak, try tightening the leaking connection with a pipe wrench, but be careful not to over tighten the connection. If the pipe connections or valves still leak, call a professional service person.
An oil furnace has an entire new set of the problems from the ones we've just conquered in gas furnaces. Move on to the next section to learn how to clear a blocked fuel line or change an oil filter.
Now, let's examine how to troubleshoot and repair an oil furnace.