My propane company lit the pilot light and the heater won't start. They said the millivolts are fine, the thermostat won't close and gas volve will not open for main burners and I need a new thermostat. Someone mentioned that there may not be enough pressure from the filter. How do I know how much pressure I need and how do I check it? Anything I should check before paying $300 to have it fixed? Thanks for any help in advance.