Dryer switches from sensor dry to 17 min, on time dry it just doesn't heat up

you could have bad gas coils.if the timer doesn't advance in auto dry most likely you're having heat problems,when the dryer heats and then the heat shuts off then the timer will advance,when the heat comes back on the timer stops,it does this until the clothes are dry.gas coils when starting to fail will work normally until they get hot and then no heat until the coils cool down then they will work again,on time dry the timer just keeps counting down until the time runs out no matter what's happening to the dryer.i've seen the coils fail after the first 10 minutes and other times for 20 to 30 minutes but usually if the load is big and in time dry the clothes will feel warm and you'll need to dry them a second time to get them fully dry,also while you're in ther you should clean out the dryer at least once a year,clean out the duct that the lint filter slides into,vacuum out the cabinet where the motor is and blow out the vent line,if it's a long run i use a leaf blower to blow out the line,remove it from the back of the dryer,stick the leaf blower into the vent line and blow it out,i've blown out birds nest out of some lines, your clothes will dry on time,you won't go through so many parts and you won't have to worry about a dryer fire,the gas coils are on top of the gas valve,remove the two phillips screws,lift off the cover and change out the coils.next time you use the dryer keep an eye on it,after it runs for 20 minutws start checking it,you'll hear a click,then another click and the flame will lite,look into the gas tube and if the flame isn't liting then you have bad gas coils.

this is a good site and should help, Tim:

http://www.applianceaid.com/gas_dryer.html#noheat

When a gas dryer starts and the burner does not stay lit more than one minute the flame sensor is not detecting the flame to as a by design safety feature the burner is automatically shut off. It is not sensing flame so it is shut off.

This is the most likely suspect. http://www.repairclinic.com/SSPartDetail.aspx?s=t-mdg5500aww-%3d%3di2681&PartID=2681

BEFORE you change this part make sure that the outside vent flapper and the ducting form the back of the dryer is free of lint. Disconnect the dryer vent and try it with nothing connected to the dryer. Also check around the lint filter area for lint especially in the bottom. If there is not a lint or ducting problem then by all means change the flame sensor.

Thanks for using FixYa!

Kelly

It turns out it was a clog in the vent. We purchased a new vent kit and the clothes dried properly.
Thank you so much.

For a gas dryer:
Assuming the dryer is working properly and the control cycles are ok, look for things like a restricted venting system which inclides the exhaust, lint screen, etc. This would be the large pipe connected to the dryer exhaust that vents outside.

If it's an electric dryer, there could be issues with heating elements, thermostats, a control board, the timer, etc. Also check for any excessive lint build-up.

you have thermistor failure/ located inside machine reason for premature heat

Could be any number of things .. igniter ( which lights the fire that dries your clothes) over-temp switches ( that disable the gas valve from opening and won't let a fire get started..) Defective gas valve.. not opening to let gas in for the fire that dries our clothes..
Those are the main components in your system and not much more I can provide to you unless I had specific details on what you've checked etc.. maybe this link will help identify the parts associated with your dryer... and if your so inclined..can do your own diagnostics... http://www.pcappliancerepair.com/model-display.php Hope that helps...

you have to change out the timer motor...
http://www.partselect.com/repair.aspx?appliance=dryer&part=dryer-wont-heat

If you use dryer sheets, LG recommends no.  Dryer sheets cause a film that will not allow the sensors to feel the clothes moisture during the drying process thereby causing the computer to countdown the timer quickly.  To clean out the sensors, use a green pad and scrub the sensor bars inside the dryer drum.  That should remove the film left by the dryer sheets.