Kenmore 110.70212990
For a Gas Dryer:
1: Check if the igniter glows, if the igniter glows for a short time, followed by a distinct "click" then shuts off, you most likely have to replace the valve coils.
2: If the igniter does not glow at all, you will need to check some electrical components with an electrical meter. (or "ohm meter"..)
First check the thermal fuse, typically mounted either on the blower housing, (for dryers with a bottom lint trap) or on the rear bulkhead, (dryers with a lint screen on top). If the fuse reads OL or infinite resistance, (open fuse) replace it and check for clear venting and proper airflow at your exhaust duct. If your venting is unrestricted, also replace the operating thermostat or thermistor, whichever your dryer has.
If the fuse checks ok, then check the the igniter by disconnecting the in-line wire harness from the igniter and reading across the two pins in the harness, if you read infinite resistance, replace the igniter.
If the igniter checks ok, read across the radiant sensor mounted on the side of the burn tube, you must remove at least one of the wires from the terminals for a correct reading, again, if infinite resistance, replace.
If this doesn't help you may be looking at some electrical issues in the temp select switch, etc. Hope this helps.