THIS BASEMENT FIREPLACE , ALTHOUGH USED SELDOMLY, HAS BEEN FLAWLESS. THE PILOT IS LEFT ON AS WELL AS THE POWER TOGGLE BELOW THE DROP DOOR, SO I'D SIMPLY TURN THE DIAL ON WALL THERMOSTAT. (2 WIRE, TEMP ONLY, NO ON/OFF SWITCH) TEMP STAYED PRETTY ACCURATE , TURN TO 65 FIREPLACE WOULD SHUT DOWN AT OR NEAR THAT UNTIL RECENTLY. YESTERDAY, WARMED THE BASEMENT FOR A CLEANING AND DIALED DOWN THE THERMOSTAT TO LOWEST SETTING (APPROX. 40 ON OLDSTYLE MERCURY STATS) WHEN FINISHED. THIS WAS THE NORMAL OPERATION, I WENT TO BED. THIS MORNING I WAS SURPRISED TO FIND THE FIREPLACE STILL RUNNING WITH THE STAT READING 75 WHEN IT WAS DIALED ALL THE WAY DOWN. I TOGGLED THE SWITCH UNDER THE ACCESS DOOR OFF AND THE MAIN BURNER SHUT DOWN. I THEN PROCEEDED TO VACUUM ENTIRE ACCESS AREA (BURNER ASSEMBLY,BLOWER HOUSING, ETC.) AS WELL AS CLEANING ALL ELECTRICAL CONNECTIONS. AS SOON AS I TURN THE TOGGLE BACK TO ON IT IGNITES THE MAIN BURNER. I HAVE NO THERMOSTATIC CONTROL. CAN ANYONE HELP DIAGNOSE THIS SUDDEN CHANGE IN OPERATION. HONESTLY, I THOUGHT THE WALL STAT WAS FAULTY INITIALLY, BUT NOT SURE. I DISCONNECTED 1 WIRE TO THE STAT WHICH HAD NO EFFECT. ANY INPUT WOULD BE GREATLY APPRECIATED. THANK YOU.