The heater usually either works or it doesn't.. some of the newer units do have stagedin heaters and run different on different cycels.. this model though i believe has a standard heating element... i would start by checking the exhaust vent and when i say checking i mean inside the dryer tube in the rear of machine and all the way where vent goes outside... on some houses they would put what was called r50 vents with screen in them and over time the lint would build up in the end of dryer run adn start causing moisture back in line and therefore increase dry time... if yours goues to side of house or through siding then check luvers for birds nest or any debri... sometimes a coat hanger works great for testing whats inside... if all that looks good i would gain access to heater area and there is a thermostat that cycles the heater on and off at temperature this may be getting weak and shutting off prematurely or not coming on each cycle allowing heater to function ... hope this was helpful to you.... good luck,,,,