Lgr 8620 pwo gas dryer cycles and heats 3 or 4 times then igniter glows but no gas or ignition. Leave dryer off for 15 to 20 minutes re-start and burner works for 3 or 4 cycles and then igniter heats but no gas.

Gas Dryer no heat: or shuts down soon after heating CHECK:

Thermal Fuse
If the air flow in the dryer is restricted, the temperature in the heating chamber can get hot enough to blow the thermal fuse. If the fuse blows, it cuts power to the coils that control the gas valve. The fuse is usually mounted to the exhaust duct just inside the back panel. You can check its continuity with an ohmmeter. If, after disconnecting the fuse, you get any reading other than 0 when you touch the leads of the meter to its terminals, it has blown. There's no way to restore it -- you'll have to install a replacement.

Igniter and Gas Valve Coils
TEST with a multi meter: The igniter is an electric conductor that works like the element in an electric heater, glowing hot enough to ignite gas when you turn on the dryer. This conductor can burn out, and when it does, it may glow, but it won't get hot enough to ignite the gas. At times it may give a reading of continuity yet fail mechanically and not get hot enough to ignite flame though it gets hot and glows and even may show Ohms or continuity ( close circuit) ?
Occasionally, the Gas safety valve and the electric coils that control the gas valve are defective -- they can wear out when the dryer gets old. When this happens, the igniter glows, but gas never enters the heating chamber or does not stay consistant.
Performing a continuity test on either part will help you determine whether or not you need to replace it. But the coils should also be tested for amount of resistance as well as Ohms. As they may be showing ohms yet not putting out enough resistance to keep proper gas pressure flowing. Most coils should show at least 1300 ohms ( GIVE OR TAKE 150 OHMS). Anything significantly less Thus u get an ignition but then it soon goes back out. The flame does not stay lit.

Air Flow and Heat
The motor that drives the tumbler also drives a fan that circulates air through the heating chamber and the tumbler and expels it through the vent. If the air can't circulate, perhaps because of lint blockage, the heating chamber overheats, which prompts the cycling thermostat to turn off the gas. The thermostat resets when the chamber cools, but the chamber heats up quickly and the thermostat again shuts off the gas. The result is that the temperature in the tumbler doesn't stay hot, and your clothes take longer to dry, if they get dry at all.

Warning
There's a big difference between a dryer that doesn't heat up at all and one that just doesn't get hot enough to dry your clothes. In the first instance, the problem is usually a defective part, and things should be back to normal after you replace it. In the second instance, the problem is caused by restricted air flow, and you need to clear the lint filter and vents and take steps to prevent lint build-up. If you don't, you'll use more energy for drying than you need and the dryer may continue to malfunction. Worse, you may have a dryer fire.

Check Igniter, Igniter Sensor (Senses Igniter is glowing) & gas valve Coils. Remove Front or rear access panel to observe/access these items. Set heated dry cycle & start dryer while observing Igniter, should start to glow bright orange for several seconds, sensor should send millivolt power to valve coils that will CLICK opening valve producing blue flame for heat. If Igniter doesn't glow within a minute, its bad, If it glows & nothing else happens it's either Sensor or Coils are bad, check the coils by using Ohm meter across plug ends of coils, if bad you will get no reading on meter, coil is open & no good, or take both Sensor & Coils to repair shop and have them tested. All 3 are accessable thru access panel opening.

From the description you give the most likely cause of this problem are bad gas coils or a bad gas valve.

You say you see the flames for 10 minutes before it stops heating but you don't mention if the igniter is continuing to glow. One thing we need to know is if the igniter continues to cycle on and off when the dryer stops heating.

There is a small square plug on the front panel you can remove to try and visually check if the igniter is glowing.

The problem won't be the thermal fuse or one of the thermostats. Once the fuse is open the dryer won't heat but it won't start to heat after 20 minutes.

After the dryer runs ten minutes and stops heating then check if the igniter is still cycling on and off. This is important because if the igniter is working then the thermostats and igniter are okay.

When the igniter glows at some point you might hear a click and the igniter would stop glowing. The click is from the flame sensor and after the click and the voltage is removed from the igniter at the same instant the voltage is applied to the gas coils and you should get a flame.

You might hear a hum, buzz or vibration from the coils when this happens. If the coils seem to react to the voltage but there is no flame then most likely the gas valve is bad. If the coils don't do anything then most likely the coils are the problem. The gas valve and gas coils can work for 10-15 minutes and then heat up and stop working till everything cools down.

One other thing I must tell you about the gas coils. Here is a link to the gas coils you will need. These are the new style that will last quite a bit longer the the older one. The coils are like the spark plugs in your car. The will need replacing in time due to wear. Below is a video to walk you thru the repair process.

You-Tube video "RjonjNitfVk" placeholder