Gas Dryer Overheating

Introduction

Does your dryer get your clothes to beyond dry? Do they come out so hot you can't hold them? Does it smell hot? This is the place to walk through the possible causes. Most of them have to deal with a dryer that either can't shut off its heat source or can't regulate the temperature correctly. If your dryer overheats and then doesn't heat at all, you should go to our Dryer Not Heating page for the causes.

First Steps

We look at airflow issues first as they are common causes of overheating.

Before you start looking at the dryer itself, is the dryer often very full of clothes or towels? It may just be a case of an overloaded unit impeding its own airflow. Check your owner's manual for proper loading capacity.
Is your dryer in a small room with little ventilation? If the dryer can't pull in air from elsewhere, it can't exhaust it to the outside, and the heat will build up.
- Usually the bottom of the door to a laundry room is trimmed to make sure there is an air gap, or there may even be a vent in it.
- Has something been done that would close that gap? A new door or floor covering that is thicker and narrows the gap can do it.
- Did your door have a vent and now doesn't?
- If any of these things have changed, your dryer may be starved for air. Open the door to the dryer area and try running a load and see if that cures the problem.
The next one is pretty simple (or so it would seem). Is your lint filter really clean? There is more to really cleaning a lint filter than just swiping off the lint. Here's a link to the filter cleaning process.
Are your dryer exhaust ducts possibly plugged with lint or other things (leaves, bird nests, toys, acorns, etc.)? Have you cleaned them recently, or ever? Here's a link to duct cleaning info.
Have you cleaned the area inside your dryer where the lint filter is installed? There can be clogs just past the lint filter in the housing. Here are some ideas of how to check and deal with that. Look at the bottom of the linked section.
There could be something obstructing the blower inside your dryer, like a piece of clothing or lint buildup that needs cleaning. Here's a link to cleaning the blower.

Next try running your dryer on a setting that should not have heat, like Air Fluff or such.

Does it heat up? If it does, you now know that you are dealing with a dryer that can't shut off its heat source.
- On a gas dryer with a timer (it has the knob you twist to set cycle times) this points to a bad timer with stuck contacts.
- On an electronic control gas dryer this points to a stuck relay on the control board.
If it doesn't heat up, then you know you are likely dealing with some other component. We will walk through those below.

Causes

Faulty Cycling or Operating Thermostat

This device controls the heat level in the dryer. If it fails, there are a number of things that can happen.

Are all the heat settings feeling too hot? This points to a sticky or failed thermostat that isn't opening when it should. You can test it by removing it from the dryer and using a digital probe thermometer and a hair dryer or a hotplate with a digital temperature readout. This is the hair dryer method:
1. Hold the thermostat in a clamp or vise so you can clip the meter leads to the switching terminals. They usually are located at the ends of the thermostat.
2. At room temperature, the thermostat should show continuity
3. Blow air at the thermostat toward the metal side, while holding the thermometer probe in the airflow right next to the thermostat.
4. Depending on your dryer, the thermostat should operate (break contact) between 135 and 165° F. You can look for a marking with an L followed by 3 numbers to tell you the temperature.
5. If it goes more than 5% above this temperature, it's bad and should be replaced
6. Here is more detailed information on testing your thermostats.
Are only the lower heat settings feeling too hot? This points to a faulty Bias Heater which fools the thermostat into thinking that the dryer is hotter than it is. When it doesn't work, it's like having the heat set to high all the time.
1. You can check this by removing the thermostat from the dryer and checking the resistance on the two terminals that are located on the top of the thermostat.
2. If you get zero or infinite resistance, the unit is bad. You will need the tech sheet for your dryer to find out the correct value, usually between 3200-4000 ohms. If it doesn't match, replace it.

Thermistor Failure

If your dryer has digital readouts, it likely uses a thermistor to signal the control board when to turn the heat on and off.

If it fails you may get an error code on some models.
To test it you will need the spec sheet for the service manual for your dryer model so that you can get the correct resistance reading.
Use a Multimeter to check the resistance reading at room temperature.
If you wish, and have the resistance values, you can check the resistance at the normal operating temperature as well using a similar procedure to thermostat testing.
If the values are off, replace the part.

Moisture Sensor Malfunction

If the moisture sensor malfunctions, it is possible for the dryer to keep trying to dry a load of dry clothes. It can make the clothes come out overly hot.

Since the sensor works by sensing the amount of moisture in a load of clothes as they touch it, if it has a short between the metal strips, it can trick the dryer into continuing to dry the clothes.
This will occur only on non-timed cycles, as the timed cycles will just run for the set amount of time.
Clean the sensor with rubbing alcohol and a cloth; sometimes there is dirt that conducts and acts like wet clothes.
After cleaning it, check the sensor for continuity between the strips, if there is a reading, the sensor is bad and must be replaced.

Hi-Limit Thermostat Failure

Occasionally a failure in the Hi-Limit thermostat can contribute to overheating.

If your cycling or operating thermostat tests bad, test the Hi-Limit thermostat as well.
The testing is similar to the procedure for the cycling thermostat.
A heat gun must be used in place of the hair dryer since the Hi-Limit thermostat operates at a higher temperature. Here is detailed information on this testing.
If the Hi-Limit Thermostat won't open at the proper temperature, replace it

Air Leaks

An air leak immediately upstream of the blower can introduce cool air into the air that is passing by the cycling thermostat, causing it to register the temperature in the dryer as lower than it actually is.

This can be caused by a leak near the point where the blower sucks air from inside the dryer drum.
Occasionally the felt seals on the dryer drum can be worn enough to allow this leakage, but this is unlikely. Sometimes there can be a leak in a poorly assembled lint filter housing.

Bad Control Board

This is the last place to look, as there is no practical test to run, you just replace it. An electronic control dryer that produces heat on a no-heat setting should have the control board replaced as there is likely a stuck relay.