I did search for posts about intermittent heat, but all I found was one for no heat (for Estate dryers). If I simply missed a relevant post, I apologize for double-posting, and please direct me to the post. Otherwise...

This could be Model #EED4100WQ. Couldn't quite make it out when I was upstairs and didn't have my glasses. Sorry. I can get it if needed, but they seem pretty much the same.

So, there is intermittent heat. My mother normally uses/used a certain cycle and sometimes the clothes dry fine, and sometimes they don't dry and she says they don't even feel warm. I always use a different cycle and hadn't noticed a problem. She switched to using yet another cycle and didn't have a problem...until today. When one load dried and one didn't, and the one that didn't apparently didn't have any heat. So the problem could be getting worse.

I read about what to do/check, and here's what we know:
The dryer vent was cleaned out--from the outside of the house, we went in with a vacuum and cleaned it out. There did not appear to be any build-up, though. We haven't cleaned the hose at the back of the dryer (yet) but because there was no build-up, and we can feel plenty of air coming out when operating, it doesn't seem likely that that part is clogged and causing the problem. (Also, it's intermittent.)

Circuit Breaker/s -- doesn't seem likely, as it runs okay (1 breaker, I guess) and the "no heat" is intermittent, so the 2nd breaker must be fine.

Yes, it's in a closet. But this is a recent issue and, again, it's intermittent, so being in a closet must be fine/it must have enough ventilation/space.

So it's down to a thermostat, a fuse within the dryer (?), a heating element (there may be more than one?), a thermal limiter (no idea what this is), or a burnt wire. There has been no burning smells, so it doesn't seem likely it's the last one.

Of the other possibilities, which could cause an intermittent problem?? Or is it something else that I haven't been able to come up with?

Related questions --

1) I'm pretty sure my dad has an Ohmmeter, but does it have to be a certain kind? I haven't fully read that post about testing for continuity, but I will. Although first I need to know where those parts are and how to get to them.

2) Of those possibilities (of what could be wrong), do you (APP) carry the part/s?

3) Is it something that I could replace/repair on my own?
3b) If so, where can I find a schematic/diagram to guide me?

Thank you for any help provided!

Here are your parts
Parts for Estate EED4400WQ0 Dryer - AppliancePartsPros.com

See the attachment for the wiring diagram.

I will try to answer your questions.
The biggest hurdle here is that the problem is intermittent so trying to troubleshoot the problem will be difficult to say the least.In my experience intermittent problems never occur when your are at the unit ready to troubleshoot. Also often just moving the unit a little can make it operate correctly.

I would unplug the unit and check the line cord connections at the terminal strip at that back of the unit. make sure all 3 connections are tight and that there is no signs of overheating. Check the prongs on the line cord for signs of arcing and that they are nice and clean.
If OK
You could check all the wiring in the heater circuit path for a loose connection. This will be a fair amount of work so if you do open it up also check the belt, the rear support rollers, the idler wheel, the front drum supports etc. You may as well give it an overhaul and at least know what a total cost to do this would be.
I would probably just replace the timer as it is the most likely cause but this is a gamble.

[COLOR="Blue"]She switched to using yet another cycle and didn't have a problem...until today. When one load dried and one didn't, and the one that didn't apparently didn't have any heat.[/COLOR]
This points to a timer problem.

[COLOR="Blue"]We haven't cleaned the hose at the back of the dryer (yet)[/COLOR]
I would check this just to be sure that it is OK.

Also in the circuit is the centrifugal switch on the motor and timer contacts A-B.

Circuit Breaker/s -- doesn't seem likely, as it runs okay (1 breaker, I guess) and the "no heat" is intermittent, so the 2nd breaker must be fine.
[COLOR="Blue"]So it's down to a thermostat,[/COLOR]
Possible

[COLOR="Blue"]a fuse within the dryer (?),[/COLOR]
There are actually two thermal fuses in the unit.
One is called a Thermal Fuse it kills power to the motor.
The other is called a Thermal Cut-off it kills power to the heater.
It will not be either of theses as they are fuses and once blown stay blown.

[COLOR="Blue"]a heating element (there may be more than one?),[/COLOR]
There is only one main heating element.
There is another heating element but it is built into the control/operating thermostat. it is turned on when you use a low heat cycle. it adds heat to the thermostat which causes it to open more often resulting in less heat from the main heater.

[COLOR="Blue"] a thermal limiter (no idea what this is),[/COLOR]
Could apply to either a thermal fuse or hi-limit thermostat.
Does not really matter as this term is not used in this unit.
[COLOR="Blue"]
or a burnt wire. There has been no burning smells, so it doesn't seem likely it's the last one.[/COLOR]
I agree with you but could be a loose connector.

Of the other possibilities, which could cause an intermittent problem?? Or is it something else that I haven't been able to come up with?

Related questions --

[COLOR="Blue"]1) I'm pretty sure my dad has an Ohmmeter, but does it have to be a certain kind?[/COLOR]
No, as long as you know how to use it. Though I am not sure it will be of any use as the problem is intermittent.
Although first I need to know where those parts are and how to get to them.
See the parts breakdown. Note that if you click on a part's picture or description a new page will open with more info about that part. There are even some videos.

[COLOR="Blue"]2) Of those possibilities (of what could be wrong), do you (APP) carry the part/s?[/COLOR]
I did look at your added post and fairbanks56 has identified the most likely cause. I would check the connectors at the timer to be sure they are OK/tight. Also the connections in the heater circuit path. If all OK then I would replace the timer.

3) Is it something that I could replace/repair on my own?
You should be able to do this if you have some DIY skills.
[COLOR="Red"]Be sure to unplug the unit when working on it.
240 volts is lethal.[/COLOR]
[COLOR="Blue"]
3b) If so, where can I find a schematic/diagram to guide me?[/COLOR]
See the above info.

It will probably end up costing a minimum of $200.00 to get a repairman in to replace the timer.

[COLOR="Blue"]line cord
you mean the...power cord, right? just check the power cord itself, and where it connects? that i can do.[/COLOR]
Yes and yes

[COLOR="Blue"]will it be fairly obvious if there's a problem? otherwise i might not know what i'm looking for.[/COLOR]
I cannot say depends how lucky you are.

so, off to find instructions on checking the timer connections and/or replacing it.
and i shouldn't need an ohmmeter! LOL. (i think my dad just has a battery tester--for small household batteries--and i doubt that's what i'd need.)
With luck it now is not an intermittent problem.
So if all else is OK then here is how I would go about troubleshooting the timer.
You will need a meter.
Run a cycle where you get no heat.
Open the door so the unit stops.
Unplug it.
Then check contacts A to B on the timer, should be 0 ohms.
If not the timer is bad.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.
4. When you start always short the meter leads together. This will tell you that the meter is working and if there is any 0 offset.

There is a good STICKY at the start of this forum about it's use

another update --

i realized i probably needed to have the dryer in the middle of a cycle to check the timer continuity?? we left the dryer mostly apart, but i put the timer knob back on and turned it to the middle of a cycle (heard it click and all). set the ohmmeter to RK1 (or whatever--the lowest for Ohms) and made sure that when i touched the leads, it went to 0.

then i checked the A to B connection, and the needle didn't move at all. i know it probably can't matter where i touched the leads to the prongs, but i tried it all over. the needle didn't move at all.
i tested it in each of the 3 cycles (using the knob to move to each one, and hearing the "clicks" as it moved). no movement at all.
from the schematic, it looked like there's supposed to be a circuit from C to H, so for kicks i checked that. still nothing.

i even checked the wires themselves, in the harness. still nothing, which is probably good, because maybe that means i wasn't a total idiot--the dryer was still unplugged, otherwise maybe the ohmmeter would've exploded in my hands, i would've blown backwards to shatter the wall mirror, and instead of being here posting, i'd be on my way to the hospital. or morgue.

and i did get the other wire harness/clip off. yes, one wire was black; the other white with a black or blue stripe. there was a tab, but rather than pushing down on the tab, i had to slide a tiny screwdriver under the white box on either side of the tab and push up. so that came off. then i rechecked the A to B circuit, but still nothing.

solved!

we got the new timer and put it in. i checked for any other damage or loose connections when i had the back panel off. didn't see anything. after install, there was heat for 2 loads of laundry, with mom using the cycle that had completely stopped having heat.

only one strange thing--just before we put the new one in, dad decided to check the new one for continuity since the meter was right there. on the new timer, the needle did NOT move when checking from A to B. then he checked from C to H, and still nothing. then he was just moving the leads around, and we got a zero Ohm reading from B to C.

we looked at the schematic, and there is a route there, but it's a bit "different" so i didn't really pay any attention to it. (btw, just so you know for others, there was a wiring schematic tucked into the back of the dryer, next to the timer. it's the same one you attached here.)

when we tested the old timer, from B to C, we also got a 0 Ohm reading. which kinda freaked me out.

i don't understand it, and i'm only telling you because maybe you'll understand it and maybe it will help someone else in the future.

at any rate, with the new timer, there is heat in all 3 cycles. so far, lol. i'm holding my breath just a bit because it WAS intermittent, at least when i started this thread. but i'm pretty sure we got this fixed.

thank you SO MUCH for all your help! you've been awesome!!