my shenandoah fp-i insert....heres my problem...it has a rheostat type dial for the fan speed....when i turn it to manual and high it blows good..but if i turn it down any at all u can hear the fans turning at low speeds but not realy moving any air....think the rheostat needs replaced or is it the blowers?...my guess is the rheostat....it is thermostat controlled...had the cover off this morning and held a lighter to the thermodisc and it would kick on but not moving air....just hear the fans churning...but again works on high and manual..