My Tassimo is 2 years old, used daily. Been descaled 3 times in those two years. Suddenly, yesterday, it quit functioning predictably. Put a T-disc in, close the "lid" and it might start on its own, then never quit. Try it again and you may have to press the start button, but it will quit in a few seconds - way short of a cup. A third try may get no result or a totally different result. The bar-code scanner is clean as are all of the other parts. It may make less than a whole cup or fill a 16 oz yogurt container (really! and I had to stop it manually, then)

Hello -

I suggest you read the Tassimo descaling information here:
http://shay.la/descaling-your-tassimo-on-the-cheap/

Best wishes.

fill it with clr and run it 2 times,then run it with fresh water each time 2x to rinse it,save the clr it is still good,use a water filter on the water

https://www.tassimo.ca/en/customer-care/#product-manuals-and-guides

at the above link you will find tassimo manuals
and yes you do need the yellow disc as it has the right bar codes for the descale cycle.
If the manual for the model you have is not available, just read one of the manuals descale sections to refresh your memory, I know I forget how in between descaling sessions

I found that my local appliance parts place (Reliable Parts) had them for about $7 each which was quite a bit less than ebay sellers and direct from Tassimo.
(Make sure yours is not hiding in its slot on the back of the machine.)_

I looked up your problem and found the same one was answered previously on fixya. I have copied and pasted the previous answer here for you. Good luck and I hope you have a great day!
After many months, I solved the problem of the red light staying on the Tassimo Coffee Maker. Use these easy steps.
1. Fill a 2 cup measuring cup with hot water.
2. Mix in descaler.
3. Pour in the empty water tank.
4. Put the yellow cleaning disk in the chamber and close chamber. Put the two cup measuring cup under the spout.
5. Push and hold the brew button for about 3 seconds (until the red and green light flash.
6. Now don't touch the machine. It will do it's thing for about 20 minutes. (Don't be impatient and start to push buttons, just leave it)
7. When it finishes it's cycle. The red light will turn off. Then clean the water tank and put fresh water and run clean water through the brewing cycle 4 times. Your machine is now ready for use.

Use what the brand recommend.
You are only asking for trouble if not.
Believe me.
This is part of my daily work.

Greetings from
Certified Bosch Siemens tech

In order to keep your Tassimo machine operational at full order, it is important to descale it every three months. Descaling products are widely available from stores that sell coffeemakers and espresso machines. Be sure that the product you buy to descale your Tassimo machine is intended for this specific use only. Mix the descaling product directly in the water container, following the instructions provided on the descaling packaging. Then replace the water container on the machine. Place a large cup or mug on the cup stand, insert the cleaning disc, bar code down and close the brew mechanism. As soon as the AUTO light illuminates, press and release the start/stop button. This will fill the brew cycle with descaling solution. Empty the cup and let the machine stand for 15 minutes. Then open the brew mechanism and close it again, leaving the cleaning disc in place. Repeat this step two more times for maximum descaling effectiveness.

Discard the remaining descaling agent from the water container, rinse it well and refill with fresh, cold water. Clean the machine by flushing water through it in the same manner and emptying the cup as it fills. Make sure that all the descaling solution has been completely rinsed away, and then flush two full water containers through the machine before using it again. Remove the cleaning disc, rinse and refill the water container and your Tassimo machine is ready to use. Also, before you descale your Tassimo machine, always unplug it. Also, never immerse the appliance in water and nor should you use abrasive cleaning products or scouring materials on any part of your Tassimo machine. This method works for most espresso machines, including some of these popular models: the DeLonghi Magnifica EAM3200S, DeLonghi Magnifica ESAM4200S, DeLonghi Perfecta ESAM5400, Gaggia 74507BCN Classic, Krups EA8080 Espresseria Automatic, DeLonghi PrimaDonna ESAM6600, the BC0255 DeLonghi coffee machine and the Krups Nespresso CititZ XN 7006.

I just spoke to Customer Service at Tassimo and they informed me that any descaler can be used as long as it does NOT have vinegar. It can be a liquid or powder and just follow the instructions on the packaging. Hope this works for you.

After many months, I solved the problem of the red light staying on the Tassimo Coffee Maker. Use these easy steps.
1. Fill a 2 cup measuring cup with hot water.
2. Mix in descaler.
3. Pour in the empty water tank.
4. Put the yellow cleaning disk in the chamber and close chamber. Put the two cup measuring cup under the spout.
5. Push and hold the brew button for about 3 seconds (until the red and green light flash.
6. Now don't touch the machine. It will do it's thing for about 20 minutes. (Don't be impatient and start to push buttons, just leave it)
7. When it finishes it's cycle. The red light will turn off. Then clean the water tank and put fresh water and run clean water through the brewing cycle 4 times. Your machine is now ready for use.

Removing the red descaling light is simple.
1. Fill reservoir with half vinegar and half water (no need for the special descaling product from Tassimo).
2. Turn on machine.
3. Insert yellow cleaning disc found in back of machine.
4. This is where most people have the their problem...You must hold the start button for 3 to 5 seconds for the descaling program to start. Both green and red light will flash.
5. Once started, use a large cup to catch the output of water.
6. The machine will cycle through the descaling program in about 30 to 45 minutes. Be paitent!!!
7. Once completed, run many cups of plain water through the system to remove the vinegar taste.
8. Red light problem is solved.

Hope this works for you.