How do I drain the water from a Bosch w135-9 water heater?

you dont drain theses type water heaters

Bosch Dishwasher Overflowing . You find your answer here. There are some parts to complicate that are easy to address.

This is a "point of service" tankless water heater that was manufactured by BOSCH. BOSCH is now Bosch-Climate.us. Technical support is available at 866-330-2729. P.S. check this site: http://tanklesswaterheaterz.com/bosch-ae-9-5-powerstar-1-5-gpm-point-of-use-indoor-tankless-electric-water-heater-reviews/

Bosch 1-866-642-3198; 800-642-3111
Copy following links to narrow down cause for EA error code:
http://waterheatertimer.org/pdf/Bosch_EA_error_code_troubleshooting.pdf
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Aqua star service bulletins
http://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/

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

Yes you need to delime tankless each year.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf
http://waterheatertimer.org/pdf/Rheem-De-lime-tankless.pdf

Contact Bosch for exact repair information. My records show following number for tankless gas: 800-642-3111
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

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

The tank is drained by removing tank, and using hot water outlet as a drain.
Under-counter tanks are not made with thick steel hull that adds cost and weight to product.
Water heater can rust out quickly if anode rod is not checked and replaced each year.
Anode rod depletion is faster if home has water softener.
All tank-type water heaters have replaceable anode rod that protects tank from rusting, and most water heater manuals include general description of anode and maintenance.
http://waterheatertimer.org/Replace-anode-rod.html#ariston

Rusted water heater must be replaced.

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Question posted under Boasch tankless. Model number not known.
Before calling service technician, open following link for Bosch troubleshooting resources, including phone and contact for Bosch, error codes, and possible manual, plus hours of reading and research:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

As you know from reading manual, tankless water heaters require yearly maintenance by trained service technician, or by homeowner. This action would check gas and pressure, venting draft, condensation drain, burner and combustion parts, igniter and-or pilot light, electrical connections, air intake and general condition of plumbing.
Problem you describe does not include error code.
Open following link for possible help with general plumbing problem:
http://waterheatertimer.org/pdf/No-Error-Code.pdf

Add a comment with model number that appears on side of unit, and I can directly locate possible service bulletins and further troubleshoot resources available at Bosch for possible do-it-yourself diagnosis and repair.

If you have hard water the unit may need to be drained and cleaned due to build up inside the tank

is there a pet **** on the bottom under a plastic cap? you might have to take the cover off and I would recomend putting some boiler drains in the line for future draining,, all units of water heaters have drains and looking at the picture I see something sticking down on the bottom see if thats not the drain