36 | Maintenance and service
• Inspect heat exchanger fincoil 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
• Check water level in the condensate trap, see fig. 34.
• If appliance is out of service for more than 10 days, fill as described on
• Check for debris and clean if needed.
Winterizing for seasonal use
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 be blank.
2. Shut off gas supply to heater.
3. Shut off the water supply to the water heater using installer supplied
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
5. Disconnect inlet and outlet water pipes from the water heater. Place a
small bucket underneath the water heater to catch residual water
remaining inside the water heater.
6. Using an air compressor, blow short bursts of air (100psi max)
through the inlet water connection until there is no water present
coming through the outlet water connection of the heater.
7. Reconnect water fittings and return heater to service when danger of
freezing has passed.
Mineral scale build-up
Periodic descaling may be necessary in areas with high mineral content
in the water. Scale buildup in the heat exchanger may result in lower flow
rates, error codes of A7 and E9 and boiling sounds in the heat
A water softener is required if the water hardness exceeds 6 grains/gal
(103 mg/l) calcium carbonate.Damage to the water heater resulting
from hard water/scale deposits will not be covered under warranty.
Descaling using a pump
▶ Disconnect electrical supply from the water heater.
▶ Shut off the water supply to the water heater using (installer supplied)
▶ Open hot water taps to drain and relieve pressure from the plumbing
▶ Drain water from the unit's heat exchanger by disconnecting inlet and
outlet water connections from the heater.
▶ Connect a line (A) from the outlet of the circulating pump (installer
supplied) to the inlet water fitting on the water heater (see fig. 64.)
▶ Using another line (B), connect the water outlet fitting on the water
heater. Route the other end of this line into a descaling reservoir.
▶ Using a 3rd line (C) from the descaling reservoir, connect to the inlet
side of circulating pump. Install a filter on the end of the line in the
▶ Make sure all connections are "water tight.".
6 720 644 887 (2013/02)
▶ Fill tank with descaling solution so both lines inside are submersed.
We recommend a straight white vinegar solution. If using a
commercial descalant, refer to manufacturer's instructions for proper
▶ Operate the circulating pump.
▶ Make sure there are no leaks and the solution is flowing from the
descaling reservoir through the heater and returning to the reservoir.
▶ Run solution through the heater until the solution returning to the
descaling reservoir comes out clear. (Changing to a fresh solution may
be necessary during this process).
▶ Disconnect all lines and drain all solution from heat exchanger.
Properly discard of solution.
▶ Position a container below the hot water outlet and connect cold
water supply. Open cold water supply shutoff valve and flush heat
exchanger with clean water.
▶ Shut cold water shutoff valve and reconnect hot water supply to the
▶ Reconnect electrical supply to unit, open water shutoff valves, and
return the unit to service.
Condensing heat exchanger unit
The condensing heat exchanger unit must be checked once a year by a
qualified and trained technician. If repairs are needed, the repairs
should be done by a certified Bosch technician.
Fig. 65 Condensing heat exchanger unit
C 1210 ES/ESC