Report "The Dayton 3E290 wall gas furnace we have is quite old. About 6 months ago we replaced the gas valve as the valve nob was malfunctioning. Usually we only set the regulator adjustment to 3 and we are toasty warm. Lately, we have had it up to 9 or 10, the highest it will go, and only get about the same amount of heat as if it were only set to 1 or 2. Are there areas that can be or should be cleaned yearly. Is there a filter on these units that should be replaces or cleaned? I do not see anything in the operating instructions and parts manual that tell me this information"