Mineral Scale Build-Up; Adjusting Co2 - Bosch 940 ES Installation And Operating Instructions Manual

Maintenance and service
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.
8. Empty condensate trap.
7.3

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 exchanger.
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) shutoff valve.
▶ Open hot water taps to drain and relieve pressure from the
plumbing system.
▶ 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. 59.)
▶ 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 descaling reservoir.
▶ Make sure all connections are "water tight.".
▶ 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 dilution ratio.
▶ 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).
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▶ 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 water heater.
▶ Reconnect electrical supply to unit, open water shutoff
valves, and return the unit to service.
Fig. 59
[1] Pump
7.4

Adjusting CO2

The CO2 can only be adjusted by a certified gas technician
with a calibrated CO2 analyzer.
CO adjustment is required in Natural Gas installations where
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energy content is less than 900 BTU/cuft, and in installations
with repeated unresolved EA and EC errors (ref. to page 60
"Problem solving").
CAUTION:
▶ One factor that may affect CO
pressure. Please see chapter 4.14 for the procedure to
measure gas pressure and record your findings below:
940 ES – 6 720 644 930 (2019/09)
levels is improper gas
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