Bosch C1050ES is tankless water heater that is equipped with the motorized water valve to adjust the water flow rate by reducing or increasing it, in relation to the selected temperature of hot water.
If the temperature of hot water is set too high for demanded water flow, the water heater will close water valve, and if reducing the temperature, heater will open valve and increase the water flow rate. A minimum water flow that allows water heater to work is 0.5 GPM, so if the flow rate is lower than that, the tankless unit won’t start.
The most common error codes that appear on the display due to the water valve failure are CA and E2. Below are the instructions on how to replace the water valve and what tools to use.
Phillips head screwdriver, grease, towel and the bucket.
Turn the water supply OFF to the water heater, on the main valve.
Turn OFF the power by unplugging the power cord of the unit.
Remove the front cover by taking off the two screws from the bottom and rear of the unit.
Loosen three screws from the control module and put it in the service position, which is horizontal.
Now you will be able to see the water valve, located on the right and above the control unit.
Close both inlet and outlet shutoff valves, usually found under the heater, and installed to separate the unit from the rest of the water lines.
Open the pressure relief valve located on the hot outgoing pipe to release the pressure.
After the pressure has been reduced, remove the cold water connection and use the bucket to collect water while draining all water from the tankless unit. Ensure that no water comes in contact with the sensors and control panel.
Unplug wire connectors (two sensors) and the main wire plug connection from water valve.
The water valve is connected to two pipes, side and bottom and has two clips. Remove them both.
Lift the water valve up to separate it from the rest of the assembly.
If the water heater is equipped with the water filter which should be installed inside the water valve, clean it from debris.
Get the new water valve and make sure it is not damaged.
Clean and lubricate the two O-rings.
Install the new water valve by connecting it with the side pipe first and bottom after.
Put the pipe clips back.
Check if there is a leak. Improper seating or damaged O-rings are the main cause of water leaking. Fix it if needed.
Reconnect the main sensor and other wires to the water valve.
Open the inlet and outlet shutoff valves and check again for leaks.
Put the control unit to normal vertical position, secured by the three screws.
Resume the power.
If everything is OK (no error codes and water leaks), put the front cover back.
For detailed instructions use pdf from Bosch site.
(Photo credit to Bosch)