Bosch GWH 1600 PS Owner's Manual page 19

Maintenance and service
6. Using a 3rd line (C) from the descaling reservoir,
connect to the inlet side of circulating pump. Verify
there is a filter on the end of the line in the descaling
reservoir.
7. Make sure all connections are "hand tight."
8. Fill tank with descaling solution so lines inside are
submersed. We recommend a straight white vinegar
solution. If using a commercial descalant, refer to
manufacturer's instructions on dilution with water.
9. Operate the circulating pump.
10. Make sure there are no leaks and the solution is
flowing from the descaling reservoir through the heat
exchanger and returning to the reservoir.
11. Run solution through the heat exchanger until the
solution returning to the descaling reservoir comes out
clear. (Changing to a fresh solution may be necessary
during this process).
12. Disconnect all lines and drain all solution from heat
exchanger. Properly discard of solution
13. Position a container below the hot water outlet and
connect cold water supply. Open cold water supply
isolation valve and flush heat exchanger with clean
water.
14. Shut cold water isolation valve and reconnect hot
water supply to the water heater.
15. Open water isolation valves, and return the unit to
service.
Fig. 25
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