Will heat water at low flow rate but at high flow rate it pulses off and on with no hot water cut flow back and it heats water hot with no pulseing off and on

SOURCE: bosch hot water service 16p burner shuts down

a tankleess water heater doen's have a piliot? but check the vent outside make sure nothing is blocking it, if it detects the exhaust thru the cold air intake it will shut off and over heat, other then that it would have to be the control board

SOURCE: Bosch Aquastar 2400E LP Does Not Heat Water

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

SOURCE: Replaced thermocouple on Bosch TF250.

Before calling service technician, open follow links for troubleshooting resources.
Bosch site does not show TF250, but shows 250SX and 250SXO.
Gas Products Technical Support: 800-642-3111
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/tabid/370/Default.aspx

At no time when visiting tankless website have I read suggestion that people fix tankless as a do-it-yourself project. In fact each site says repeatedly to call service technician for installation and repairs.
When reading service bulletins, the repair protocols are generally long and very sequential, even if a thermocouple seems straightforward there are many interrelated parts and sensors that must communicate exactly with each other.
Example: following pdf outlines operation sequence for non-standing pilot model
http://waterheatertimer.org/pdf/Tankless-gas-operation-overview.pdf

The dirty water also suggest that tankless has not gotten regular maintenance that is required for continued operation. Tankless are not install-it-and-run-flawless-for-years type of machine.
Read manual for specific maintenance required for your model. For example yearly flushing the heat exchanger with vinegar to avoid lime build-up is suggest most models. Tankless are succeptible to lime build-up.
All costs are energy. Maintenance alone can easily eat up the promised $1-8 monthly savings from tankless vrs tank-type water heater. One service call can wipe away years of expected savings, plus replacement part can sometimes cost as much as whole new tank-type water heater, installed.

SOURCE: powerstar 115 tankless tripping reset

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

SOURCE: water doesn't stay hot PowerStar AE3.4

Apparently the software in the brain of the unit is not capable to modulate for smaller heat need and it trigger off the unit when it only need less the 20F temp increase . That is a lack of engineering in the brand unit, and really can not be "fix"