I have a Mr Coffee MRCTB and it does not stop the heating of the water. Replaced the high limit switch and it did not do the trick.

SOURCE: water is not heating

It is probily the thermal switch between hot wire and element. Check to see if you are getting power through this switch.

SOURCE: MR COFFEE FTX49. Brewing starts, then stops

Mine just started to do the exact same thing. So I decided to clean it using the "Clean" program and just water. I put the brewer through the cleaning program 3 times - each time it would brew water from 12 cups to 8 cups, I'd tap the brewer on the countertop, it would brew from 8 cups to 4 cups, tap it again, and it would brew the remaining cups. So, I called the Mr. Coffee help line (800-672-6333). The most-likely problem is that the hose is no longer attached in the water reservoir. The help line suggested that I take it in to a service center. I live in Urbana, IL and the closest service center is in Oak Lawn, IL - 2 hours away from me!!
Here is my solution:
1) Buy another coffee brewer.
or
2) Smash your current Mr. Coffee brewer into a million pieces (this relieves stress) and go buy another coffee brewer (probably stay away from Mr. Coffee products).
Hope this helps.
Frustrated in Urbana

SOURCE: I have a Mr Coffee MRCTB and it does not work

You don't. It stays in there inside the heating tank. When you put in cold water, it pushes out the already-hot water. Every year or so, you need to clean it out, or have someone do it for you. I just cleaned about a half inch of gunk out of one we have had at the fire station for about 10 years. Never knew we were supposed to clean it out...yuk. Tastes better now. Clean as a whistle! Also had to replace an overheat safety switch, $8.00 on-line.

SOURCE: Mr. Coffee FTX45, worked yesterday. The display

If you have an ohmmeter take the bottom of the unit off and check the thermal fuse for continuity that is the most common failure. It's located inside an insulated tube and clamped to the side of the heating element. If that is ok another clamp secures the thermostatic switch usually a porcelain body. When cold it should be closed or show zero resistance. The thermal fuses are available at Radio Shack but replacing it requires it's leads to be welded because solder melts at 350 deg F.
I have replaced them successfully by using crimp connectors available in the electrical dept. of your nearest auto supply. Hope that helps.

SOURCE: My Mr Coffee ADX20 coffee

You might have scale that formed on the heating element. This happens to all heating elements due to impurities in the water. I would try cleaning it a couple times to see if it helps first! Clean the mineral deposits from your coffeemaker every 80 brew cycles if you have soft water and every 40 cycles if yours is hard water. About once a month is good for a coffee maker. Pour four cups of undiluted white vinegar in the water reservoir. Place a paper filter into the removable filter basket, close the lid. Go through a brew cycle with decanter in place. Turn the coffeemaker OFF after THREE cups of vinegar have entered the decanter. Let set 30 minutes. Turn machine on and let rest of vinegard run through. Discard filter and vinegar solution, rinse. If this doesn't help the element is probably bad and from everything I have heard Mr. Coffee doesn't have't replacement parts for consumers. They only sell to "Authorized" repair shops. With that being said I have heard if you call the Service number 1-800-672-6833, and talk to an human operator, not the machine, they have sent out new units because of this problem. If that doesn't help Coffee makers are usually throw away items, I have recently purchased a pretty nice Mr. Coffee one from Costco for $30. Kohl's had one the looked a little different but all the same features for $55. So for like $30 you can get a new one, where if you could find an heating element it would be probably around $20. Just saying!