Dryer turns but doesn't heat

The heater turns on when conditions are met;
1.) thermostat is allowing it to
2.) over-temperature device is allowing it to
3.) mode selector switch is allowing it to
4.) heater coil is continuous and not broken

let's focus on number 2. some dryers have a self-resetting device that "repairs" itself after temp drops to safe level. others have a fuse type device that must be replaced if over temperature occurs. First, test for AC voltage at the heater.terminals. if ac present, heater is broken or has faulty connection. If no AC, remove power from unit and test resistance across each device listed above. Ohms for each should be as close to zero as possible except for #4 which should be about 2-5 ohms.