I have a Alex Duetto and have had many different problems that parts took care of. but, for the last year or longer my brew temp probe keeps getting lime buildup and then the pid control does not operate correctly and no hot water.
I stopped using the machine in 2015 for 6 months and then replaced the probe on 8-23-15. I finally bought Dezcal and used it one time. Then probe worked a couple months and stopped again.
Today 6-3-16 I decided to try and get the machine going again. I removed the probe and it has very small amount of lime deposits. I am going to see if I descale the machine again will help? If not? Does anyone have an idea how to cure my ongoing problem? I know, replace the probe again. But, it costs money to replace the probe every three months.
I have city water that has been tested and is very low hardness. Then the water goes to a whole house water softener with separate water filter line to the plumbed in Duetto. Chris Coffee has no answers to offer me?
Any suggestions?

It sounds like you have a water problem to me. You may want to use a separate water softener and filter for your machine's water. Is it plumbed in? If so, you can get a softener and filter to connect to the plumb line that should help. If not and you're just using tap water to fill your tank, you might want to get a bottled water with low hardness, like Crystal Geyser.

Also, leaving the machine unused with water in the boilers may be contributing to the problem by allowing scale to build up from disuse. If you do leave the machine unattended for long periods of time, it's probably a good idea to drain the boilers first.

According to the Orrville Water Department your finished water is moderately hard at just 98 ppm total hardness.

I first bought the Duetto II Septembe, 2008 and much of the time would leave it running all day so I could have coffee anytime I came home without warming up the machine for 2 hours. Within a few months of operating on internal tank, I had professional water softer installed along with filter to take out the chlorine taste. I never had much problem with the probe. But, have replaced many of the other components of this machine. If your are not a technician, espresso machines are not especially a good idea. During all the advice of replacing PIDs, pumps, gaskets, seals, valves, etc, it was never suggested to descale the machine, only back flush through the portafiller. My first time to descale was 8-23-15 after searching my problem on the internet. I then installed a new probe. That worked fine for a few month. And I only operated the machine about once a week. Spring of 2016 it worked a few times and stopped. I quit.
I gave up and went to the Areopress and our Bonavita coffee machine. Today I decided to try to revive it once more.
The temp heated properly to the PID temp of 200 and I descaled the machine according to LattaLove's U-tube directions.
It seems it is working as designed again, If it continues to heat properly I will descale it every 90 days and see if the barnacles stay off the probe. I also have taken one of the top stainless steel covers off to let more heat escape from the machine. Thanks for your replies. I still like drinking espresso or Americano as a way to test my coffee roasts.
Schlonegerscoffee.com

That's very strange. I had the exact same machine for about four years, and I never once had to descale it. I was running it off one of the softener/filter combos that Chris' Coffee sells. In fact, I never had any serious problems with that machine, and our local water is quite hard.

I'm not sure why yours is so prone to scale buildup, especially if you have a good softener and relatively soft water. I wonder if you should try running it off the internal tank using water known to be less hard. Descaling every 90 days or so should not be necessary, and may lead to other problems, like failed seals and valves if crud gets into them from the descaling.

Descaling my Duetto II only lasted one day. Yesterday the Temp reading on the PID was all over the place and one time read 163 degrees. So, maybe the machine is ready to be scraped? Is 7 or 8 years maximum for Espresso machines?

No, a quality machine like yours should last many years with proper regular maintenance. Things will fail from time to time, but there are few problems that can't be fixed if you are willing to do some work. Alternatively, you can take it to an authorized dealer or shop that can do the work.

It sounds like maybe some of the electronics (maybe the PID?) are failing on your machine, but this is something I would want a qualified person to diagnose and repair.

I know some of the Duetto's had bad PID's. Co worker has an old one and had issues with the PID losing all of its settings and going crazy. The vendor confirmed they had a bad batch and replaced it. You may want to contact the vendor you purchased it from and ask their advice. A new PID should not be very expensive. Last one I purchased was around $35. The machine itself should last decades and your water hardness is no where near bad enough to descale every few months. I have around 140ppm and do it once every year and the machine runs 24/7. You have a different issue going on.

You started with " my brew temp probe keeps getting lime buildup and then the pid control does not operate correctly and no hot water"..
Then you commented it only lasted one day after descaling...

Puzzling. I have one of the first Duettos, had a PID that died, never had scale issues, temperature has been rock solid.... But you could remove and clean the probe and see how that works (you may have tried that recently as you stated). Also check that you don't have wiring issues (take a very close look at the connections between the pid and sensor). If cleaning the probe (and in absence of interconnect issues) doesn't have the desired effect for a period of time it would seem prudent to replace the PID.

Your temp control is only one element in a very well equipped machine. Don't replace it unless you are done with working the issue...A new machine will likely present you with new challenges, but they will be new

Also, the Duetto 2 did not come out till mid late 2009, so maybe you have a Duetto 1, although it really doesn't make much difference except that in the 2 both steam and brew are controlled by the PID, rather than just the brew temp, with the steam controlled by a pressurestat in the 1.....

If you have a 2, then does the steam pressure act erratically?

Since you are talking to Chris' ....try talking to Tim in service....hes been there with the Duettos since day 1.....