Our second unit just failed and needs a new controller more money

Depends if you have new or old style energy smart.
Generally this can mean the control board is bad.

Link below has contact information for Craftmaster and Whirlpool and some troubleshoot resources:
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

Repairs are funneled through the manufacturer who profits by selling non-generic parts not available from local hardware store... with purpose to end DIY repairs, make more money for manufacturer, and build up network of brand-loyal repair service companies who can sign you up with a repair package ... under the banner of saving you $1 a month in energy cost.
Look at label located on side of water heater to find manufacturer and serial number.

If water heater is within 6-9 year warranty period, then parts are covered, but labor is not.
Manufacturer can send parts and/or refer you to local technician.

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

All resets and breakers trip with high heat.
Do you mean the tankless unit is tripping the 40 amp circuit breaker?
Or the thermal cut-out, located on unit, is tripping?

Is this a new installation?
Or was the tankless working before and stop working?

Copy following link to check wiring.
AE 9.5 requires 40 amp breaker and 6 gauge wire.
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

If the unit is tripping the thermal cut, -out, then product manual says to call Bosch or service technician.
Call Bosch 866-330-2729
http://waterheatertimer.org/pdf/Bosch-Powerstar-AE3.4-7.2-9.5.pdf
Thermal cut-out can trip if water flow is too low.
Try changing power selector screw from Hi to Lo so only 1 element is ON. See diagram page 6 of manual.
Adjust the 'outlet service valve:' The manual recommends that a ball valve be installed between hot outlet and faucet. Adjust the valve so more water flows to faucet.
Remove aerator, clean aerator, don't use low flow restrictions or low flow shower heads, replace leaky faucet cartridge on single-handle faucet.

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

Bosch has 10-year limited warranty.
Probably the seller honors warranty first 90 days and Bosch afterward.

I think warranty is similar to car warranty where parts are covered, and they pay for parts to patch up the blown transmission but not give you a new car. But I hear of cases where the company just send a whole new Tankless unit and you install it yourself.

Contact Home Depot and present them with receipt.
Contact Bosch with the same information given in Fixya question.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Add a comment and say why unit broke down first time, and add what resolution was reached to help others with same question.

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.

Is it flashing 2-3? Try this: You can reset the control by unplugging the blower during start up, leave unplugged for at least 5 seconds, plug back in and within 30 seconds cycle temp control from hot to low 6 times.

Certain water gas water heater models feature electronic controls with a flammable vapor sensor installed on the bottom portion of the water heater unit. This sensor is designed to shut off your water heater system to prevent fires in case flammable vapors are present within the area. If your flammable vapor sensor caused your water heater to shut down, check the area immediately for leaking gas or other flammable products. Common household chemicals such as bleach can also trip the safety system as well as unsuccessful burner ignition attempts. I'm not sure what control your unit has, but on a White Rodgers here's how it goes.


White Rodgers Intelli-Vent PowerVent Control Equipped Models

1. Step 1 Turn the water heater's blower switch off and disconnect the power cord for the water heater (refer to your particular model's operation guide for the exact location of the blower switch). Disconnect the Molex connector attached to the bottom of the control pad (the left most connector with five pins).
   
2. Step 2 Turn on your multi-meter and set it to read resistance or "ohms". Connect one of the multi-meter's probes to the number two pin and the other probe to the number three pin of the Molex connector (middle black wires). If the reading on your multi-meter reads below 9k or above 45k ohms, the flammable vapor sensor is faulty and in need of replacement; you cannot reset the system until this issue is resolved.
   
3. Step 3 Reconnect the Molex connector to the bottom of the control pad, reconnect the water heater's power if and turn the blower switch to the "ON" position. Press both the left and right buttons on the control pad at the same time. Wait for the green light on the control pad to blink and press the following buttons in sequence: Left, Right, Left, Left, Right, Left, Right, Right (you will need to perform these actions within 30 seconds of reconnecting the power cord to the water heater in order to be successful

I am a RV service tech and that is an old unit. Your control board is bad but with the age of that unit I would strongly suggest replacing the whole water heater, you can shove a pile of money at it and still have an old water heater when for 3 to 500 bucks you can have a new one with a 2 year warranty

EC is no ionisation and is usually the result of a gas pipe or gas supply pressure problem. The other problem is the installer never adjusted the CO2 levels. If the yellow paint on the two screws inside the cabinet is still intact, the plumber did not do his job. Make sure this is done with calibrated CO2 analyzer that was calibrated within the last 6 months.

sounds like your gas lines are too small or not enough pressure... or you may have to clean the rods

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

The water heater is locked out. The following process should reset it.
1. Reapply power to the water heater and wait for 3 seconds for the system self-diagnostic check.
2. Within the first 30 seconds, the temperature dial must be rotated back and forth crossing the 120
degree mark at least six (6) times. This will reset the control and display a normal flash code
(slow blinking).