Calcium buildup on heating element. It's unmovable.

Couple of ideas.

Your weak coffee could be due to the machine not getting hot enough, which is usually caused by calcium scale buildup on the heating element (the "burner").

Try descaling with a citric-acid based cleaner, such as Dezcal or Durgol.

The second is the coffee your using is a weak blend. Try changing to a different coffee and see if the strength is better.

calcium will stick to heating element 1st and make it less able to heat water , eventually it will consume the entire surface and insulate the water from touching it and warming it and finally overheat it and cause burnout , high calcium (limestone) is usually a condition that occurs when filling via a well or stream , consider getting a load of pre softened water from a municipal water system , there should be a list of haulers in your area that can provide this service

This could be a heating element going out do a ohms check on the elements

ADD SALT......

I think your problem is the buildup, which would cause your elements to work much harder trying to heat the water - especially if you have well water as opposed to chlorinated city water, although city water still has calcium, etc. in it.. Add a whole house filter to your water line where it comes into your dwelling - there are a myriad of elements available at varying microns to catch the calcium
and other contaminants. These filters normally need changed every 3 months - I would check your after a month to see what it is catching. These whole house filter systems are not expensive - check out your local hardware or plumbing store, I'm sure they can guide you to the proper set up ( after you verify what they say through some online research) . Better safe than sorry !!
p.s.there should be 2 elements in your water heater - 1 above and 1 below, so after you've installed your filter change both elements - I'm sure you'll find they last a lot longer!! Also - before you cut off water to your home for the install, fill up a clean 5 gallon bucket and RINSE the filter element , then turn off the water supply to your water heater to prevent a loss of prime and water hammer to the pipes.

Check the elements first, also check the hi-limit switch and the thermostat, then check the elements the machine might have been low on water at one point.

I created a tip sheet to help with this, let me know if you have questions beyond what is in this link.

http://www.fixya.com/support/r4666624-hard_water_calcium_white_powder_build_up

You can clean the calcium/lime build up with CLR and a scotch brite pad.

Limescale is mostly calcium or magnesium carbonate and will dissolve in acid. If you don't want to use the commercial limescale removers you could try soaking the element in vinegar, or lemon juice, or coca-cola and then rubbing at the residue with a plastics pan scourer. (Wrap the element in some cloth and keep basting the cloth with your chosen remedy for a few hours before trying the scourer.) If you can reduce the dishwasher temperature below 55C this will help a lot in the future.Hope this helps a bit!
I'm sure you know how this site works - everyone wants to be a guru and only Fixya! ratings are worth having. If my offering doesn't work for you, just forget the rating :-)
Thanks in advance D.

Get some c.l.r. (calcium,lime,rust) remover at a supermarket.Add a cup and run a cycle,this should solve your problem--repeat if necessary.