OK, DV (millivolt systems) experts...I've got a baffler. Got a customer with an older Gas Technologies, Inc gas fireplace. This company was the precursor to Heat n Glo... Not a very aesthetic unit...Flames are all the same size & the logs are concrete... Anyway, I digress... Like I said, it's a millivolt system T-couple/T-pile & the unit works fine, burns nice & steady Mv readings are 550 +/- on the pilot & 220+/- with the burner on... Perfect, right? Once the blower comes on, the millivolts on the t-pile drop like a rock... I mean quickly... Within 2-3 minutes, the burner will shut right down... If I turn the blower rheostat off, the mvs climb back to normal... This unit has a spill switch wired into the valve/t-pile/rocker switch system, so I rewired the the system to eliminate any potential grounding due to the deteriorated sheathing... Still the same results... I took the thermo-disc out of the blower system & still the same results... I unplugged the fan & turned the rheostat on & the mvs held true... I turned the rheostat off & plugged the fan into the "hot" (unswitched) receptacle, & the mvs held true... I don't have the know-how to test the rheostat or the blower to determine which one is (or BOTH ARE) the culprit... Any ideas where to check next?