How to change transducer - Bosch PowerStar AE115 Tankless Water Heater...

sounds like you had issue before if you replaced transducer then, i replace it again

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

If you change motherboard on laptop computer ... do you expect it to work flawlessly afterwards?

Call Bosch for service manual.

Tankless computers that heat water are problematic for folks... evidenced by working at fixya.

Buy tank type electric water heater at Lowes for 285 and be done with it. Saves money long haul and repairs can be made same day with generic off the shelf parts from hardware store, and unit can be maintained to last forever.
http://waterheatertimer.org/How-to-maintain-water-heater.html

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

Control unit or flow transducer. If the transducer(impeller in the clear tube) is spinning freely with waterflow, then the circuit board needs to be replaced.

9:10 times the control board is bad. You are wise to suspect as much.

If you smell it - look fer it. It may be a bad connection on the AC supply line all the way back to the service panel or inside the heater connection panel. Bad connections cause high heat and discoloration of wires or connectors and a serious voltage drop to the appliance.

I don't have specific suggestion for tankless tripping breaker or if that is a circuit breaker problem or a tankless problem.

1) Move wires to another same-size breaker and see if problem persists.

2) Compare amp draw on tankless label with wire size and breaker size amp rating.
For example 30 amp breaker using 10ga wire is rated for 80% of listed amps or 24 amps.

3) If you are drawing full 30 amps, then 30 amp breaker is getting hot. Breaker trips with heat. Older breakers can trip more easily.
http://waterheatertimer.org/How-to-replace-circuit-breaker.html

4) Before calling service technician, open following link for Bosch troubleshooting steps.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

5) Be sure to read manual for yearly maintenance requirements.

6) Add a tempering tank for incoming cold water problem.
http://waterheatertimer.org/Tempering-tank.html

7) All gas tankless brands can be repaired by homeowner for $330.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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.

turn the temp to it;s lowest setting and isolate it from the other unit till it fires up, let me know if this doesn't work,, [email protected]

It sounds like you have a copper canister unit. Ohm out the elements in that one canister. the directions are on the websight for bosch, or I can walk you through it. But you will need a digital multimeter to do this. If you have a blown element in that one canister, then the tco will not reset.