My machine won't let me choose the brew size even though it shows "brewing ready" and after 4 minutes or more it may work.

had the same issue as you do, unplug the unit. I let it sit unplugged for about a minute and then plugged it back in. Suddenly, it appeared to be functioning normally again. The screen indicated the full range of brewing size selections and when I selected my size and hit the brew button, it actually drew water from the reservoir, then it brewed a nice hot cup of water. It's been working fine ever since

You should call your vendor for service on any commercial brewer. (Especially if it's on loan from them)
*** the following is for information only as all repairs should be performed by a qualified tech.***
* There is an on/off heater switch located in the back of the brewer. This should be on when the brewer is needed. There will be a 20 minute wait for the "ready" to brew light comes on. If you brew before the light comes on then the coffee will be only warm.
* If everything is on and looks okay but it takes forever to light the ready light then the main heater is not working. Call your vendor for service.
Aloha, ukboy57

P.S. The 3 liter brewer has a much larger tank than the regular 2.5 brewer. So expect it to take a bit longer to reheat a full brew. Some customers will request the 'Airpot' or 'Pump pot' to be filled to the top which means even more water is needed to be heated. Expect at least a 20-30 minute wait on reheating. I've found that customers that use this large a pump pot will brew +3 pots in a row. (Regular, Decafe, and a 2nd regular or 'flavored' coffee.) Often brewing without waiting for the ready light. If this is the case then mention this to your vendor. You may need a 2nd brewer, larger brewer, or have the brewer hooked up to the 'Hot' water line to get pre-heated water to the brewer (though they may need to modify the water valve to one that is rated for hot water inlet line.). If your using larger 3L decanters then having pre-heated decanters and using the 'pour over' function can aid with faster brews. Though this method is a lot of work for the operator.

Clogged exit port from heater section. Clean as per manual page 18.

Hi, It needs to be serviced. Sounds like a few things going on wrong. Clogged brew unit most likely. Dazza REPAIRER

Hi,

Here is a tip that I wrote that will give you some things to try that will helpyou get your Keurig coffee brewer workingagain.

Keurig CoffeeBrewer not making a full cup of Coffee
heatman101

Hi,

Here is a tip that I wrote that will give you some things to try that will helpyou get your Keurig coffee brewer workingagain.

Keurig CoffeeBrewer not making a full cup of Coffee
heatman101

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Hi
You must make sure that the brew unit is ready to reinsert into the machine. To return the brew group to the centered position, you first need to drop the funnel. To do this, look on the opposite side of the brew group from the handle. At the top you will see an object that looks like a sharks fin. If you follow this piece down you will see 2 horizontal bars on the brew group body. Push your finger between these 2 bars and the funnel will drop. Now you can push the puck slide on the left side down and to the center. If you look down through the funnel you should see a piston. This should be centered in the funnel. If not, locate the slide on the left side of the brew unit, (it should be hanging down, a flat rectangular piece attached to the cylinder) and push the slide to the right until it does. Push the press button and you are now ready to reinsert the brew group in to the machine. First you must close the door with the drip tray and dredge drawer inserted and turn on the machine without having the brew group in. You will hear the motor turn on and when it stops completely, open the door and remove the tray, and dredge drawer, now replace the tray and insert the brew group. If it still won't go in check the cog in the back of the machine. There are 2 wide teeth that should be at the 10:00 and 12:00 position. If they are at a different position you have a broken drive gear.

Open the brew mechanism. Opening the brew
mechanism will initiate the heating of the water and the
HEATING light will flash.
2 Place a clean cup on the cup stand, adjusting the height of the
stand up or down so that the rim of the cup is close to the
brew mechanism.
• To adjust the cup stand, insert your finger in the center
of the stand, lift and turn.
• To avoid spilling over, please choose the right sized cup for
the drink you are making.
3 Position your choice of T-DISC on the T-DISC holder, label facing
down. Firmly close the brew mechanism by pressing the clamp
down until it shuts. The HEATING light may flash again as the
machine heats the water to the required temperature for
your drink.
4 When the AUTO light illuminates, press and release the start/stop
button. Brewing will start automatically. There may be a short pause
during brewing; this is normal and is designed to draw out the full flavor
of your drink. The AUTO light flashes throughout the brew cycle. When
the machine has finished brewing, the indicator light will move from
AUTO to MANUAL and then, after a delay of 30 seconds, to HEATING.
5 Open the brew mechanism, remove the T-DISC and discard.
Your drink is now ready to be enjoyed.
You can prepare the next beverage right away by repeating
steps 2 - 5.

it seems that it does not pump water in, after switching it to ON, it stays running for a few minutes then shuts OFF without even showing "READY TO BREW"..

What to Do If Your Keurig Won Brew Cup Barista