Electric bill doubled last month, and we've had the Powerstar AE125 tankless electric for over a year. There are no leaky faucets.

there are no valves in the unit. You can only regulate waterflow through this machine with self-supplied ball/gate valves

You need three #8 wires for AE125. Two #8 wires for AE115.

1) Copy following link for wiring information:http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

2) The AE125 has 3 elements, and requires 3 wires.Each wire is sized #8 copper, and is connected to 40 amp breaker, up to 100 feet. Over 100 feet, use 50 amp breaker and #6 wire. Oversizing breaker and wire is smarted and more efficient than undersizing.

3) Often a separate subpanel is installed to provide 3 extra spaces.

http://waterheatertimer.org/images/Main-subpanel-Tankless-600.jpg


4) Makes sure main breaker panel can accept additional 120 amps of draw without overampping panel ... and starving other appliances of full power.... that will damage appliances, overheat motors, and damage main panel and overheat main breaker. You want to oversize, not undersize electric service when installing tankless electric, which is why I do not recommend tankless electric installation, including issues of costing more to operate, and expensive repairs, and general money risk-nuisance of owning tankless vrs tank-type heater.
http://waterheatertimer.org/Troubleshoot-household-electricity.html#stress


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Heating water can peculate chemicals out of water, such as metals and organics.
Especially above 138 degrees.
Have well water tested.
Turn down thermostat temperature.
Or reasonably harmless well-water bacteria can react with anode rod, or other reaction in softener, to produce colored water, and smells.
Different water can produce different sludges, brown, red, gray, black, yellow.
The sludge can also combine with deteriorating pipe flakes to clog water flow.
Sludge can accumulate over years in low spots in pipes, or at elbows and constrictions.
Have plumber flush pipes.
Or run new pipes.
Also delime tankless yearly, and flush with white vinegar as shown in product manual, and treat bacteria with H2O2 hydrogen peroxide.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf

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

Contact Bosch 800-283-3787, or service technician.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Product has 10 year limited warranty against defects in workmanship, failed parts, failed heat exchanger for original homeowner with receipt. But does not cover neglect, failure to follow maintenance, installation etc. Pg 23 example manual
You generally have to pay for service call to verify installation, then send tankless into factory, or have service technician repair unit, at your expense minus cost of parts
http://waterheatertimer.org/pdf/Bosch-AE115-AE125_manual.pdf

To double check wiring:
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

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

Question posted under Bosch tankless.
Question says 'tank'
Brand, model, and type heater unknown.
Elements mean electric.
'Thermal cutout pops when taking shower produces cold water' indicates tankless, since tank-type would maintain some hot water.
No error code might indicate tank-type.
Add a comment with type, brand and model number of heater for possible assistance.

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

Can tankless electric water heater be repaired? Sure.
Is it worth the expense if problem is going to happen again? I can't answer, but can offer resources.

New tank-type electric water heater costs $207 and new tank-type gas costs $320 at local box store.
You can install new tank-type electric yourself in a couple hours. DIY repair on tankless is not easy since parts are not at local box store, and what part do you need, and tankless parts can easily cost more than new tank-type water heater.

Open following link for Bosch troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

GENERALLY, Tankless require .4 gpm (gallons per minute) water flow to activate heating cycle, and then require .25 gmp flow to keep heating cycle going.
For example .4 gallon per minute means faucet can fill 1 gallon container in 2-1/2 minutes
Some tankless units require more water flow, for example .75 gpm

Tankless water heaters have flow sensor that tells computer chip when enough water is flowing to activate heating cycle.
If the sensor is clogged, or if water filter inside tankless unit become clogged with dirt or sediment from hard water, then the unit does not signal enough water flow and will not activate.
Home filtration system and water softener can also slow the flow of water.
Low water pressure and crossover problem on single-handled faucet and crossover on recirculation system check valve and high thermostat setting can also cause heat cycle to not activate.

Tankless cannot be exposed to water with more than 11 grains hardness or parts inside tankless will coat with sediment and not work. Within 2 years the unit will not work, with diminished efficiency from the beginning.
http://waterheatertimer.org/Battelle_Final_Report.pdf

If water is hard, and you cannot soften the water, or if water is dirty and cannot be cleaned, then the best recommendation is to use tank-type heater instead of tankless.

All costs are energy. For average home: Tankless electric is NOT cheaper to operate than tank-type electric. Tankless gas saves $1-8 per month. However, cost of unit and installation, cost of potential repairs and cost of parts, difficulty of DIY repairs, required yearly-monthly maintenance, etc outweigh expected savings.
http://www.pmengineer.com/Articles/Cover_Story/8cf9e86f7c298010VgnVCM100000f932a8c0____

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

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

Ok, sounds like a flow sensor issue, is your house water pressure steady or does it fluctuate? The sensors on these seem to be a common issue and this model has many issues with heating. take care

Hey did you ever get this fixed mine is almost the exact same thing we've been using ours for about 3 years and today nothing. Thanks for your help.

good luck,, there aren't that many whole house electric tankless units of any kind even made