My gas furnace will go through it's cycles... turns on,ignitor glows gas comes on,then the flames then the blower blows. Gas shuts off,blower cools the furnace,supposed to shut off but it starts the cycle again.It won't completely shut off till I turn the theromostate off.Please help. Tamara

Now my furnace will run the cycle except that when the blower is cooling the furnace it will try to come back on ,as in the blower shuts off,it clicks for the ignitor to come on,it does,it clicks for the gas and flames to come on but it does not. It will try 2-3 times to get the gas and flames but it does not ignite the gas and then it will shut off. Ignitor glowes and there's clicking but no flames now. Funny thing is if I take the doors off the front of the furnace and hold the button that way the furnace will come on and go through the cycle but still resulting in the above problem;goes through cycle tries to start back up but no flames so it just shuts down. Please help. Tamara