I have had this ventless fireplace for 4yrs. so far it has been flawless. recently it seems to delay on igniting. t-stat calls for heat then propane does not ignite right away like it used to. when it does ignite there is a large 'WOOSH' of flame then it runs normal. it is not consistent, sometimes normal operation. pilot light is lit, just seems it takes a bit for it to ignite. anyone have anything like this happen?