20 Most Recent Bosch 2700ES-LP Propane Tankless Water Heater... Questions & Answers

You had service techs and Bosch techs and neither can find a solution.
I assume you want impartial opinion at fixya.
Multiple error codes and a lack of progress by professionals implies PC board failure. BUT there could be multiple problems. Error codes are considered 'start' point for troubleshooting. Beyond that, Bosch should give you contact information to a trained professional service tech >> not just a plumber, but a guy who can do the electronic diagnostic.
Open following link for Bosch troubleshooting resources.
Tankless are high tech gadgets that cannot be exposed to more than 11 grains hardness in the water, and require continual maintenance. The cost of repairs and maintenance will never pay back from the expected $1-8 monthly energy savings.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
You can solve most tankless problems same day for $350.
Then sell the tankless unit back to Lowes or sell it for parts on auction site.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Before calling service technician, open following links for Bosch troubleshooting resources and information that might help narrow down the problem(s):
No error code indicates that first suspect is a plumbing problem.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/pdf/No-Error-Code.pdf

Losing pendant displays on cool to cold mornings with your Bosch Highflow 25 EC hot water heater could be caused by temperature-related issues affecting the display module. Cold temperatures can affect electronic components, causing them to malfunction. It's possible that there could be a loose connection, moisture buildup, or a fault in the display module itself. I'd recommend contacting Bosch customer support or a qualified technician to diagnose and fix the issue.

If your Bosch Highflow 21e hot water system is experiencing fluctuations in water temperature while showering, it could be caused by a few different factors. Here are some possible reasons for this issue:

1. Flow rate too high: The hot water system may not be able to keep up with the demand if the showerhead or tap is allowing too much water to flow through. This can cause the water temperature to drop suddenly. Try reducing the flow rate by turning down the tap or using a low-flow showerhead.
2. Water pressure fluctuations: If the water pressure in your home fluctuates, it can cause the hot water temperature to vary. This can be caused by various factors, such as other appliances using water at the same time, or changes in municipal water supply pressure. Installing a pressure regulator or a flow restrictor may help to stabilize water pressure.
3. Blocked or dirty water filter: A clogged or dirty water filter in the hot water system can restrict water flow, causing the water temperature to fluctuate. Check the filter and clean or replace it if necessary.
4. Malfunctioning thermostatic mixing valve: The thermostatic mixing valve (TMV) regulates the water temperature in the hot water system. If it's faulty or dirty, it can cause temperature fluctuations. A licensed plumber or technician can inspect the valve and replace it if necessary.
5. Faulty temperature sensor or control board: If the temperature sensor or control board in the hot water system is faulty, it may not be able to maintain a consistent water temperature. A technician can diagnose the issue and repair or replace the faulty component.

If you're unsure about how to diagnose or fix the issue with your hot water system, it's best to contact a licensed plumber or technician for assistance.

The Bosch JSRZ 5-T PG tankless gas water heater may not start automatically because of problems with the magnetic sensor valve, power supply, or control unit/thermostat. Possible troubleshooting steps are:

• inspect the water inlet valve and replace if faulty
• confirm that power to the unit is functioning
• if the problem continues, seek professional repair service.

Do you live in a climate where the hot water line could have frozen? If your heater did freeze up, that could be very bad. This is because water actually expands when it freezes and can do a lot of damage to pipes and to the water heater itself. My other thought is possibly a clogged in line water filter. But typically a clogged water filter would make it run with reduced pressure rather than a complete shutdown all water flow.

https://www.fixya.com/support/t13643459-a2_af_error_codes

need control tested to find what failed

It could be the thermostat sensor They usually have a carbon buildup. They are easy to install and not that expensive. Good luck

your not making sense with you question --state it goes cold in middle of shower --but state it will stay hot or cold forever ----if its the latter continued hot till you shut off water that normal working if the unit shuts down during shower then you have a problem ----unit is set at one temp and runs at that temp and you use shower 1 handle / 2 valve what ever you own to adjust temp their are really only 4 reasons stops making hot water ----2 are usually well water supply --incoming water pressure /flow or to cold ----other are gas valve -or sensor so i would look into your shower handles since almost all have adjustments and anti scold safety

SEEMS LIKE CALLING A LOCAL PLUMBER IS BEST WAY

most likely. contact a dealer for advice

try Bosch tech support .

check to see if voltage correct if not replace board if ok bad ignitor

WOW!!! Great answer by Steve (I know Steve Spam...real name Richard). Lot of time on his hands (37000 answers). Can we get real professionals answering questions. Thank you Richard...let's just call you Dick for short.

Are you holding the flame button until the thermocouple heats up.

you dont drain theses type water heaters

you can not drain these w/ heaters