I own an old heater/furnace. Its called a Duo Therm. I have to push down the knob to light the pilot, but the flame keeps going out when I release the knob. The instructions say to hold the knob down for 1 minute. I have done this many times and it has worked. However, tonight its not working. Any suggestions would be greatly appreciated seeing how its supposed to get down to 25 degrees tonight. Your attention to this matter is greatly appreciated