After researching on line, it appears the F-24 error code is an indication of a bad heater or a bad heater relay.  The relay seems to be the more common F-24 culprit.  I found a video that was very helpful, and the first advisory was to check the heater's resistance.  I did this using a multi-meter and got a reading of 12 ohms.  The machine in the video was located in Australia, so that means 240v.  I think the reading on that heater was in the upper 20's. 

Is it safe to assume that the reading I got would indicate the heater is OK, based on 110v?  If so, then the relay is likely bad, but the video didn't provide any way to test it.  Finding a replacement locally has been futile.  Even on line the hits I got were for used ones on eBay, and they were not cheap.  I hate handwashing dishes and they've been stacking up, so the sooner I figure this out, the better.

Any advice would be greatly appreciated.  Here's a picture of the relay:

Thanks to all for the good information.

I opened up the relay housing and as you can see in the shot below, there's been some serious arcing action happening.  The contacts had what appeared to be pitting, but on closer examination there seemed to be a texture to the silvery surface on the contact points.  Without a brand new relay for comparison, I don't know if the textured surface is intentional or not. 

I think the carbon residue inside the housing is enough to indicate trouble regardless, so I'll begin the hunt for a replacement relay.  I'd prefer brand new, but may have to settle for used & tested.  I didn't think my dishwasher was so old that parts for it could be NLA by this time.  It's been doing a great job, so I'll happily pay for a relay as opposed to a whole new machine.

Henrik, thanks for the argument against the pressure switch.  I located the switch and was dreading the process of accessing and extracting it.  Melvin was right about the pressure switch video not being the best presentation, so I wasn't comfortable with pursuing that possibility.

Unfortunately, the relay isn't available on line from the Miele parts site you provided.  I've had no luck getting through the Miele USA parts site, so I've made an offer on a relay listed on eBay with the only seller who will accept returns. 

If my machine was produced in 2010, I guess 13 years is a decent run for a relay.  If it was among the last produced in 2016, not so much. 

Thanks for further confirmation that the relay is likely the source of the F24.  This information matches what I found on line:  the most common cause of the F24 code is a bad relay.

I searched for Miele parts dealers in the San Francisco bay area and got lots of hits, but when I called few of them I was told that they don't stock Miele parts.  Go figure.  It seems that the only way to purchase a Miele part is to schedule a service call through an authorized Miele service provider.  My offer for the used relay was accepted.  Although the price was higher than a new one from Miele, it's still a lot less expensive than the additional cost of sending a repair tech out.

This situation has spooked me about ever buying another Miele product, I will tell you that much.

This is where I land after I click on the link that was provided immediately above: "(h)ttps://ww4.miele.de/msd/MSD#/device/43049/etd/1836514681701"   It's almost entirely blank except for the banner info at top and some diagrams on the left, there's no item in the cart, the part number is one I haven't seen, it's not the Miele USA site and the 8th diagram doesn't apply to the relay.  If you don't arrive at that empty German Miele page like I did, something must be getting lost in the link translation between continents.  I don't know where the problem lies, but Miele USA seems not to want to play ball with me.

Thanks for trying, but I can't return the eBay relay if it clears the problem, so at this point I'm committed.

Thanks guys.  I truly appreciate all of the trouble you have gone to in order to unlock the mysteries of Miele's on line presence.   I can't even imagine using a phone to navigate their site even if I landed on the right one.  I need a full screen with a real keyboard for maximum efficiency and to avoid catastrophic blood pressure spikes. 

The relay is scheduled to arrive on Monday.  If it resolves the issue, great.  If it doesn't, then I'll attempt to test the pressure switch if I can find a better explanation on how to do it.  I'm not good with schematics or the lingo and electrical theory required to follow them. 

If all else fails, I'll schedule a service call.  That would be far less expensive than replacing the dishwasher like-for-like.

Fingers crossed that the relay due to arrive on Monday fixes things. 

If necessary, I'll try to use my phone's Google translator while I watch portions of the pressure switch video.  I wonder if I pulled it up on the YouTube streaming channel if there would be an English subtitle option there.  I'll look into it.

Thanks John.  I agree about the pressure switch design.  I will cross that bridge if I come to it, unless it's going to be an exasperating process to access it.  At that point, I'll pay for a service call.

The relay arrived this afternoon and the machine is back up and running.  It's been 20-30 minutes since I started a normal wash cycle with a full load, and the detergent dispenser just popped open.  I'm feeling pretty good about the machine running all the way through.  I've only pushed it back into its opening about half way and still need to pull it back out and put the bottom panel back on.  I'll do that before I run the next batch of dishes and other items that have been backing up.  I really do hate hand-washing dishes!

Thanks for all of the time, effort and advice that has been contributed by everyone.  I'm glad it turned out to be the easiest of the potentially necessary repairs.

The machine cut out and displayed F24 around the same point in the cycle as it did the first time.  This was sometime during the main wash because I never heard it drain again, but it's fairly quiet, I was in another room, and after taking a look inside, the tub isn't full of water.  It was definitely hot inside, so the heating system is working.

I suppose the pressure switch is the next component to check.  Maybe it will be easier to locate a new one, as I wouldn't trust a used one.

Yeah, all of that electro-jargon is over my head, and the mention of wrong info in the manual was enough to make me decide to cut the crap and make a service call.  The relay was as far down the rabbit hole as I felt comfortable going.

I'll circle back to this thread to share the findings and results from the technician visit.

Hey John,

Yes, the machine has been extracted since I started investigating the problem.  It has to be placed on its side in order to access the relay.  I only pushed it partially back into place to do a test run after replacing the relay. 

I called an authorized Miele repair service today -- no thanks at all to Miele's poorly designed customer service web site.  They are bent on making it next to impossible to find any sort of assistance with problems, sending the user in circles or to dead ends, and I am done with them in that regard.  I used Google to locate an authorized Miele repair service, found one with good reviews, and they seem to focus on dishwashers.  I have an appointment for a week from today.  

Since I've already paid for an overpriced relay that didn't resolve the trouble, I think it makes sense to stop throwing money at this issue when there's no telling whether another overpriced component will rectify the problem.  I'll leave it to the experts, and John, I know I'm preaching to the choir with that decision! 

Assuming the machine can be successfully repaired, I'll use it until something else goes wrong.  As much as I love this dishwasher, I won't pursue repairs again.  I'll find myself a nice Whirlpool/KA that offers straight-forward support, repair service and access to parts.  Miele has soured me on ever buying another foreign brand major appliance.

The repair guy (Nash) just left.  Super nice and we might even be playing on the same team. 

He got on the phone with Miele tech support and went through a lot of diagnostics, pushing various buttons, watching for display info and checking functions.  He's fairly certain it's the pressure switch, but he's ordering another heater relay just in case the one I got from eBay is faulty.  There's a chance it could be the inlet valve, but enough water is entering the machine and the heater is definitely working because after a few minutes of making it run, steam escaped when he opened the door to check water temperature.

I don't know when he'll be back, but he's competent, he's interested in understanding machines and getting to the bottom of things, he likes to talk appliances, and likes what he does.  He even checked the OTR GE microwave and replaced a bad fuse -- in exchange for some huge fresh picked lemons my neighbor dropped off while he was here.

I'll return with a full report after his next visit.

P.S.

The Miele tech was on speaker and said the correct way to work on these dishwashers is to turn them on their left side (when facing the front of the machine).  Nash said he puts them upside down.  If you put them on their right side, there's a chance for any remaining water to get into some electrical components.  Luckily for me, I made sure all water was out of the machine and stuffed towels into the sump just in case, because the video I watched for replacing the relay showed the guy laying it on its right side.

Nash returned today with a new heater relay and pressure switch.  The machine completed a "Normal" cycle without any trouble.  He also fastened the machine into place from the top with Miele screws rather than from the sides with grabber screws, which is how my plumber installed it when we moved in almost five years ago.  It was not easy to remove the grabbers and I'm glad to have the machine is properly secured. 

I hope this will be it for a while, but if any other appliance should require repair in the future that's beyond my capabilities to fix, I'll be calling Nash.  He's not only a fine looking man from Azerbaijan with thick black hair and beard but he's also very kind and sociable, and loves his work.  Eye candy is a bonus that the majority of us here can really appreciate.  I wish that man all of the success in the world.  He's very deserving and is managing to make a go of it in the most expensive area in the country.