Powerstar 45-551701 low water pressure - Bosch PowerStar AE115 Tankless Water Heater...

make sure you have the water connections right. the inlet goes on the blue side. Also, your pressure must be a minimum of .8 psi. If not there will be no hot water and the neon will be off. other possible causes might be a crossover in your plumbing or a stuck flow transducer. Here is a link to a guide to explain how to check these items. http://efficientelectricwaterheaters.com/Tech-Support/PowerStar-Tech-Support.asp

Check for crossover:
http://waterheatertimer.org/Crossover.html
Clean water filter located just above where water enters unit.
Copy following link for Bosch powerstar manuals with brief troubleshoot section in each;
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html#manual
Call service technician who is qualified to work on computer that heats water. For plumbing problems, call local plumber. These are two different things.
Fix any brand tankless yourself, same day, by replacing the whole thing. Buy electric water heater at Lowes for $285 and be up and running by sundown.
Gene
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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/

Open following link for Bosch tankless troubleshooting resources, including Bosch contact information, typical manuals, error codes, tech support, parts, fuel-saver calculator, water heater forum, fixya links, disclaimers, and for finding service technician.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

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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

The easiest thing to do would be to call Bosch and just ask for a new heater for free. The other option is to call Bosch and have them send you all new elements. If there is power, there should be heat of some kind.

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

SOUNDS LIKE THE PUMP NEEDS REPLACING CHECK IT OUT.

This is a common problem. They are desighned to come on when a certain volume of water goes through it and with todays low flow water conserving devises they don't always come on with one faucette.

You can have a loop installed that allows a higher volume of water to flow when a valve is turned on. It simply flows back into the supply side of the unit.

If on a well, you can install a regulating valve in the line to help with this problem. You may have to play with the valve a little to find the right pressure to avoid those highs and lows. I installed a Bosch A125 and had this problem from the start. A little research un-earthed the regulating valve (I think around $25 at Lowe's or Home Depot) and we have had even hot water ever since.