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.
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