I came home to find my unit off. The fan blows to exhaust the combustion chamber but the until will not light off. I turned off the unit for an hour then turned it back on and it still would not light off when call for heat. I went to bed and in the morning the house was warm and the unit is working again and has continued to work for 2 weeks. Any help with suggestions on what might be going would be going would be helpful. Thanks