I have a Heil DC90 that wouldn't start this fall, after being off for 5 months. The thermostat clicks, but nothing happens at the unit (no blower, no gas hiss, no glowing ignitor, nothing). I replaced the ignitor assy, as it had last been replaced 5 yrs ago according to the handwriting inside the panel, but still nothing. I've tried pushing down on the 4-pin plug going into the Honeywell SV9501M2726 SmartValve to make sure it's connected, but still nothing. How can I check the SmartValve?