My Powerstar tankless water heater was installed last April and we have a problem that has become a real issue. We can set the temperature where we want it and get in the shower and the water will go from what we set it, to ice cold - to very hot, can someone please tell me what the problem is and how to fix it.

Tankless promotion is certainly slick and inviting...

-Tankless gas save about $100 per year vrs pre-april-2015 gas water heater for 'average family of 4.'
-New energy standards will reduce the expected savings to $70/ per year.

-Tankless electric cost about $100 more per year to operate than ordinary electric water heater for 'average family of 4'

-Do-it-yourself repairs are generally not possible with tankless.
-Tankless gas require larger vent and larger gas line, and a condensate drain.
-Whole-house Tankless electric will probably require a new electric service panel
-Tankless require yearly deliming/ descaling of heat exchanger... and heat exchanger will lose efficiency over time because of scale... even if unit is delimed each year.
-Electronic controls are vulnerable to surge
-Only the alloy heat exchanger has long-term warranty, but otherwise the warranty is same as typical tank heater
-Tankless cannot be exposed to more than 11 grains hard water or parts can fail within 2-3 years
-Tankless might not be able to keep up with higher temperature setting needed to fill very large tub (or any bathtub) if incoming water is too cold due to winter conditions. Etc.

Example Rheem tankless resource:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pro-n-con-for-tankless-water-heater.html

Example installation for tankless electric
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

Gene


Water Heater Timers Save Money

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

http://waterheatertimer.org/pdf/Bosch-AE115-AE125_manual.pdf
Bottom page 10 troubleshoot

Add tempering tank to pre-heat cold incoming water
http://waterheatertimer.org/Tempering-tank.html

Call service technician

Delime heat exchanger.
http://waterheatertimer.org/How-to-delime-tankless-water-heater.html

Replace with tank type?
http://waterheatertimer.org/How-to-install-electric-water-heater.html
Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Water leaking into elements. Bad PC board. Undersized breakers. Undersized main panel.
Bosch Powerstar is a computer that happens to heat water.
If your 5-year-old laptop computer was malfunctioning, you would not be surprised.
But for some reason (false marketing by manufacturers?), folks believe a tankless computer is going to last 20 years.
Moreover folks also believe tankless will provide endless hot water while saving money.
The whole idea of tankless saving money is a load of sales-BS that defies physics and common sense.
There are no service manuals... except bosch website has troubleshoot section in product manual.
Call a bosch-qualified service tech.
Go to Lowes and buy ordinary tank heater, and fix your heater today for only $250.
Tank-type electric water heater can be easily repaired and maintained by homeowner to last forever... that is a fact
http://waterheatertimer.org/How-to-maintain-water-heater.html

http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Call Bosch. And exercise your 10 year parts warranty rights.
Copy following link for Bosch power star manuals:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html#Ariston
Check circuit breakers, fully off and then fully back on. Test if voltage is at least 80% rating plate on unit. Check that temperature dial is set correctly. Call for service again.
Don't install tankless computer that heats water. You cannot fix this computer yourself, and they are problematic for owners.
Go to Lowes right now, spend $285 and buy tank-type electric water heater, roll it into your house, and save money, since the electric tankless computer heater costs average $100 more per year to operate than tank-type heater for average family of 4.
Tank type heater can be repaired by homeowner same day for $25 using off-the-shelf parts from hardware store. And that empowers the regular guy, and gets you off the junk tankless treadmill.
Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

This is a "point of service" tankless water heater that was manufactured by BOSCH. BOSCH is now Bosch-Climate.us. Technical support is available at 866-330-2729. P.S. check this site: http://tanklesswaterheaterz.com/bosch-ae-9-5-powerstar-1-5-gpm-point-of-use-indoor-tankless-electric-water-heater-reviews/

Problem might be crossover from failed single-handle faucet cartridge:
http://waterheatertimer.org/Crossover.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

There are a lot of other things that eat electricity. Like space heater and using ovens for heat. Heat pump.Central heat fan running all the time. House lights left on. Outside flood lights. Clothes washer using HOT water. Look around real good. It all adds up. Also the power co. may be charging more for "fuel" costs surcharges. Here in GA I'm paying a bit more now to pay for a nuclear power plant.

You've done the required first-step troubleshooting and maintenance.
If thermal cutout keeps tripping, and unit is actually reaching 185, then something is wrong with wiring, temperature sensor, gas valve, or PC board. Or combination of factors.
Call service technician, and open following link for some Bosch tankless resources including Bosch contact information:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

try bleeding that section of pipe. or the whole system if not.

The PowerStar AE115 unit replaces the PS19T model which has been discontinued. Now's the time to upgrade...