Are little plumber electronic descalers any good

this is a water temperature problem what controls your water temp is not working

""hey Im a plumber and every tank I sell now includes the temp regulator and at 5 hours to install so why not suggest a new unit, after all a simple valve replacement and 1 hour labor doesn't amount to a decent income""
I'm not a plumber but if you are not aware of what is going on and don't get a second opinion and quote , the plumber walks away a little richer
I have explained the reasoning and hopefully given you something to think about so that if replacement unit is necessary you will know that you have not been ripped of .

I think you'd have it repaired by professional plumber. I know one plumbing company, which can deals in residential as well as commercial properties. They've vast experience in this field over fifteen years. http://www.ps2i.biz/plumbing-systems-solutions-company-info

You had service techs and Bosch techs and neither can find a solution.
I assume you want impartial opinion at fixya.
Multiple error codes and a lack of progress by professionals implies PC board failure. BUT there could be multiple problems. Error codes are considered 'start' point for troubleshooting. Beyond that, Bosch should give you contact information to a trained professional service tech >> not just a plumber, but a guy who can do the electronic diagnostic.
Open following link for Bosch troubleshooting resources.
Tankless are high tech gadgets that cannot be exposed to more than 11 grains hardness in the water, and require continual maintenance. The cost of repairs and maintenance will never pay back from the expected $1-8 monthly energy savings.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
You can solve most tankless problems same day for $350.
Then sell the tankless unit back to Lowes or sell it for parts on auction site.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Yes a local plumber should be able to do it. Finding the part however may be harder. There should be a plumbers supply company that handles commercial units nearby.

I would recommend a simple sediment filter housing be installed on the main water line coming into the house. Material cost about $100. Have a plumber install a bypass loop so you can just shut off 2 valves when you need to change it. I always install one with any tankless heater as cheap insurance against such a problem. As far as adding something to clean the lines I would refer to the manufacturer's instructions and use only what they recommend in order to preserve your warranty. For a solar water heater I prefer Velux.

Please rate if this helps-