Bosch water heater stopped heating - Bosch PowerStar AE115 Tankless Water Heater...

gas valve sticking

5 years is about the lifespan for tankless.
You might have shorted element. That would explain cooler water and tripping reset.
Test element: power is off, disconnect wires from element; ohms = voltage squared divided by watt rating of element
http://waterheatertimer.org/How-to-test-water-heater-element.html

Call service technician./ Call Bosch
http://waterheatertimer.org/pdf/Bosch-AE115-AE125_manual.pdf

Gene

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

Unplug micro switch located on bottom of water heater if it has one

Clean water filter yearly or monthly. Page 16 example manual.
http://waterheatertimer.org/pdf/Bosch-125BO-NG-LP-outdoor.pdf
Shut off the installer supplied cold water supply valve.
Disconnect water pipe going to the back of the water
valve. Remove filter from back of water valve. Clean the
filter and inspect for damage. Replace if the filter is at all
damaged. Inspect the top of the water valve for signs of
a water leak or corrosion. If present, rebuild the water
valve.
Bosch service bulletins:
http://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/38b-125-series-bulletins.html
Descale heat exchanger yearly.
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

The following link has general troubleshoot steps for Bosch A2 error
http://waterheatertimer.org/pdf/Bosch_A2_error_code_troubleshooting.pdf

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

Before calling service technician, open following link for Bosch troubleshooting resources including Bosch contact number and possible manual:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Tankless water heaters require yearly maintenance to check gas pressure, inspect and clean burner and combustion parts, inspect vent and vent drain, clean air filter, check water flow, de-lime the heat exchanger etc.
This maintenance can stop ordinary problems from occurring, and can be done by the homeowner by reading Bosch service manuals for specific model number.
The continual maintenance, and cost of repairs and parts, and cost of professional service are more expensive than expected $1-8 monthly energy savings from owning tankless.

Fix most tankless problems yourself, same day, for about $350.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Call Bosch
Gas Products Technical Support: 800-642-3111

That model number is only shown at one website, and that model number is not shown at Bosch.
Open following link for Bosch:
http://www.boschwaterheater.com/BoschHotWatercomHome/GasProducts/tabid/331/Default.aspx
Search of Bosch for that model number shows no result.

Some water heaters do not have a pilot light. Instead they use hot surface igniter rod that glows red hot
The igniter rod ignites the gas after solenoid valve opens and gas flows to combustion chamber.
The igniter rod and heat sensor have to be operational, and have to be positioned correctly for ignition to take place.
If igniter rod is not working, or if heat sensor does not detect flame, then gas solenoid valve shuts down and water heater does not heat water.

1) Call service technician, and when that person arrives, ask about tips and tricks for maintaining tankless water heater.

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

3) Add a comment with your experience so others with same problem will benefit.

4) Also 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, but does not take place of service call since you will be doing the work yourself, on a complicated appliance that is affected by perfect cooperation of internal parts, and external factors.

how is heating element ? Wasit on with no water running thru it. Does it have a reset?

Sounds like the water flow sensor and servo, may just need cleaning, get it checked out by a Bosch agent