dryer starts and drum turns but doesn't heat up .tried all settings

there is no power from timer yellow striped wire to ground on metal of dryer.

Sorry, I meant to check terminal 3 (yellow wire) at temp switch, not timer but that doesn't matter since you have power at safety switch yellow wire. Check between safety switch yellow wire and the other thermostat next to it purple wire. You say no power between those? (one meter probe on yellow wire, other probe on purple wire) Check safety yellow wire to other thermostat black wire. If you don't have it between those wires but do have 120vac to ground at safety yellow wire then looks like faulty motor switch.

Eric

Ok, just to verify, when you place one meter probe on safety thermostat yellow wire and one on control inlet thermostat purple wire, you have 120vac. This means you have power to the gas valve. Problem could be faulty ignitor, flame sensor or gas valve coils. There is a hole in the bottom panel at front about 6 inches from right side. You can use a mirror to slide under the hole to see if the ignitor is glowing with dryer running. If it is then you either don't have gas or the valve coils may be bad. If it's not glowing then either the ignitor is bad or the flame sensor is open. You will need to remove the front panel to gain access to this area for further testing.

Eric

Unplug the ignitor connector and check resistance of the ignitor. Should read about 300-500 ohms. Unplug one terminal from the flame sensor on right side of the combustion chamber and check continuity of flame sensor. Should read zero ohms (closed/short).