1

Here is what I have done for my 10 year old LG dryer that resides outdoors:

  1. checked the exhaust pipe and there was good air flow with no lint stuck in it.
  2. checked for continuity between heating element's housing and the wires coming to it - there was no continuity as expected.
  3. measured temperature at the exhaust pipe when dryer was at high heat setting with no clothes in it. It cycled between 61C(141F) and 71C(160F).

Temperature test

So far I have bought two thermal fuses from Amazon.com and both of them died in few months. Here is also a close up picture of thermistor:

Thermistor close up

What could be the problem and what additional test to perform?

Update #1: Picture of back draft flap. Seems clean to me.

enter image description here

4
  • cheap fuses from amazon? perhaps try one that's rated 10C higher; it shouldn't burn down your house...
    – dandavis
    Mar 4, 2018 at 5:56
  • @dandavis Yes, cheap, but allegedly OEM (seller is listed as LG, but shipper is someone else). Also original fuse was OEM. Not sure how to find compatible fuse that has 10C higher tolerance.
    – user389238
    Mar 12, 2018 at 5:10
  • if you google the part number, you often can find a seller offering a whole range of such parts in different cut-off temps. more expensive are re-settable ones. you might also replace it with a cheap bimetalic heat switch, the kind used in hair driers; they reset one they cool down some.
    – dandavis
    Mar 12, 2018 at 6:27
  • The thermal safetys are designed as a fail open to prevent a fire. Putting a self closing sensor may cause cover a real problem.
    – Ed Beal
    Mar 12, 2018 at 13:24

4 Answers 4

2

Replace the thermostat also, it should be right there next to the fuse. Its probably reading a little low, or intermittently failing, so the dryer is getting slightly hotter than is supported and the thermal fuse blows. Also, while you have the cover open, you can be sure to vacuum the vent and everything making sure there are not restrictions like others have mentioned. For me, the thermostat solved it after I went through about 5 thermal fuses.

3
  • Since I have cleaned the vent pipe, then I think this is one of the most likely explanations. Do you know how to test this thermostat? It says L125-31C which I am not sure yet how to interpret.
    – user389238
    Mar 1, 2018 at 22:15
  • It’s 12 bucks on Amazon so the test is trying a new one. If you’re concerned about price you can return it if it doesn’t help. I vaguely remember reading a whirlpool service manual (I realize yours in an LG but they look similar) that said to always replace both thermostat and fuse as a pair. Maybe that’s to reduce callbacks for a technician but it made sense.
    – freshop
    Mar 2, 2018 at 22:59
  • Ok, this is what I did as first attempt to address the issue. However, before I installed the new thermostat I put both of them on a temperature regulated mini-stove to see if there would be noticeably different resistances and it seemed that they acted same (ie resistance on voltmeter went from 1 Ohm to 4 Ohms for both thermostats when temperature reached 100C). Perhaps this was not scientific enough test, because multi-meter rounded values to Ohms and I did not go all the way to highest settings.
    – user389238
    Mar 12, 2018 at 5:18
1

I would check the back draft flap at the vent exit to the house. I have had these stick causing low air flow that caused the thermal fuse to blow. The second thing I have found was a buildup of sand in the bottom of the blower assembly the dryer was blowing but the sand had reduced the flow, I cleaned the sand out and some lint build up on the blower and that solved that one.

1
  • I added picture of back draft flap. Seems good to me. Anyway, good guess.
    – user389238
    Mar 12, 2018 at 5:24
1

Could this be a heating element going bad? (I assume this is an electric dryer.)

Usually they burn up which I think means you get an open rather than short the thermal fuse. But I seem to recall that when mine went bad a few years ago I replaced that fuse along with the heater element. They are not too pricey.

1
  • Do you mean that heating element could be having hot spot right where is the thermal fuse? Would you know how to prove or disprove that, because right now I have few more theories that, for example, relay could be sticking or thermostat gives incorrect reading and causes heating element not to turn off.
    – user389238
    Mar 2, 2018 at 7:13
1

My bet is the venting pipe is clogged with lint. This restricts air flow so that insufficient heat is dissipated off the element. This will cause the hi-limit to cycle. This high-limit is not designed to cycle the element. It is only a safety cut-out. This in turn will knock-out this hi-limit. The entire vent pipe assembly needs to be cleaned/serviced regularly. Additionally, I recommend replacing it entirely every 5-years.

3
  • Can you explain a little more what you mean with "This high-limit is not designed to cycle the element."? I guess in that sentence you are referring to thermostat reaching hi limit and not thermal fuse, because, if I understand correctly, then once thermal fuse reaches hi limit it will stay open forever and can be thrown out. Then what confuses my is what is supposed to cycle the heating element under normal conditions? Is it dryer's controller+relay after it reads temperature from thermostat that is below the Hi Limit?
    – user389238
    Mar 1, 2018 at 22:35
  • The main thermostat may be failed in the closed position. This leaves the hi limit controller cycling the element. It is not designed for this duty.
    – Paul Logan
    Mar 4, 2018 at 17:32
  • Wait, so would this mean that there are 3 temperature sensing elements in a laundry dryer - 1) Thermostat with writing "L125-31C" (in the picture; Today I also replaced this one for the first time); 2) thermal fuse (further back in picture. This is the one I have been replacing like 3 times) and 3) main thermostat? If so then where is main thermostat?
    – user389238
    Mar 12, 2018 at 5:23

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