I have a gas furnace that uses an intermittent pilot/ignition to light the pilot. The furnace itself is having problems starting the main burners, so I took a look. I found the following:
When I turn on the furnace, the igniter lights the pilot flame, and the igniter eventually stops after 5-10 seconds, i.e., the flame rectification system appears to be working fine. However, the main burners never start. Measuring the (AC) voltage between the main burner output (MV) and MV/PV as well as ground on the ignition control module, it appears to be nearly 0 V. Does this sound like my ignition control went bad, even if it is able to detect the pilot flame and shut off the igniter?
As a test, I unplugged the flame sensor at some point and turned on the system. I wasn’t surprised to see the igniter sparking even after the pilot flame was lit. I was, however, surprised to see the igniter never stop sparking (at least for 5 minutes), while the pilot flame continued to burn. Is this normal? It seems like the igniter and gas should have been shut off by the ignition control after at most a minute or two.
If it helps, the ignition control module’s make/model is Robertshaw SP715A. The furnace is a Williams Forsaire Counterflow Furnace model #8508332.