Maintenance and service
▶ Always shut off the electrical power supply, shut off the
manual gas valve and shut off the water valves whenever
▶ Inspect and clean the complete water heating system once
▶ Carry out a maintenance as necessary. Immediately repair
all faults to avoid damage to the system.
Annual maintenance table
Inspect venting system
Inspect combustion chamber
Inspect pressure relief
Inspect water filter
Table 35 Annual maintenance
(To remove front cover, see page 12.)
Venting system - inspect inside of flue pipe for any blockage
or restriction. Observe burner flames during heater
operation. (front cover must be removed). Burner flames
should be steady and blue. Yellow, inconsistent (bouncing)
flames may be an indication of poor ventilation or
combustion air supply. Inspect the combustion air inlet
pipe for blockage or debris. Inspect combustion air and
exhaust terminations for blockage or debris.
Inspect burner observation window (fig. 67, #14) for
cracks or spillage of flue gases. Observe burner flames
during heater operation. Flames should be steady and blue
940 ES – 6 720 644 930 (2019/09)
with no signs of yellowing. Yellow burner flames are an
indication of improper combustion. Refer to chapter 4.4,
page 33, chapter 4.3, page 15 of this manual to verify
exhaust system and combustion air supply meets
Manually open the pressure relief valve to ensure proper
Inlet Water Filter
Verify the inlet filter screen is clean and undamaged. The
inlet water filter is located on the bottom of the appliance,
to the right of the cold water inlet fitting. (See fig. 33,
page 40). Close installer supplied water shutoff and
remove wireform spring clip from filter. Remove filter, clean
and or replace if damaged.
In areas where the water supply has a high mineral content,
the heat exchanger should be flushed with a descaling
solution. Scale build up will shorten the life of the water
heater and damage resulting from scale is not covered
under warranty. Refer to chapter 7.3 for detailed
instructions on descaling the heat exchanger.
Inspect heat exchanger fin coils for soot build-up or
blockage. To access fincoil, consult service bulletin at
www.bosch-climate.us. If there is evidence of soot build-up
or blockage, the heat exchanger should be removed by a
professional and cleaned thoroughly.
The water heater must not be installed in a location where it
may be exposed to freezing temperatures. If the heater must be
left in a space which is likely to experience freezing
temperatures, all water must be drained from the heater. If
precautions are not taken, resulting damage will not be covered
under the warranty. NOTE: Use of agents such as anti-freeze is
not permitted and voids the warranty, as they may cause
damage to the water heater's internal components.
1. Press ON/OFF switch on the water heater to turn OFF the
heater and unplug power supply cord. The display should
2. Shut off gas supply to heater.
3. Shut off the water supply to the water heater using installer
supplied shutoff valve.
4. Open hot water taps to drain and relieve pressure from the
plumbing system. If water continues to flow after 5
minutes, a crossover of the hot and cold water pipes is
present and must be corrected before proceeding.
Winterizing for seasonal use
Maintenance and service