Bosch Appliances Model GWH 425 manual Main burners, Vent assembly, Mineral scale build-up

Maintenance and service

5.4Main burners

The main burner flames should be blue, with a more intense blue cone in the center core. Yellow flames could be a sign of wrong size gas orifices or dirty burners, a blockage on the heat exchangers fins. If some burners have yellow flames while others have blue flames, it is likely that dust, lint or spider webs have partially clogged the burner venturis. To clean the burners, contact a gas service person.

5.5Vent assembly

Inspect the draft hood and heat exchanger fins for signs of soot build-up or any other foreign material such as spider webs. Clean out any debris found in the vent hood. Signs of soot indicate insufficient combustion air or exhaust draft. Check for vent assembly blockage or combustion air blockage on the underside of the unit.

12.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).

13.Disconnect all lines and drain all solution from heat exchanger. Properly discard of solution

14.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.

15.Shut cold water isolation valve and reconnect hot water supply to the water heater.

16.Reconnect electrical supply to unit, open water isolation valves, and return the unit to service.

5.6	Mineral scale build-up
The GWH 425 PN, when operated at lower
temperatures settings, does not accumulate mineral
build-up. If however, the heater is used at the higher
temperature settings and the water has a high mineral
content, periodic descaling may be necessary. The
heating coils should be flushed with a descaling
solution.
5.6.1	Descaling heat exchanger
1. Disconnect electrical supply from the water heater.
2. Shut off the water supply to the water heater using
(installer supplied) isolation valve.
3. Open hot water taps to drain and relieve pressure
from the plumbing system		Fig. 27

4.Drain water from the unit's heat exchanger by disconnecting inlet and outlet water connections

5.Connect the line (A) from the outlet of the circulating pump (installer supplied) to the inlet water fitting on the water heater

6.Using another line (B), connect to the water outlet fitting on the water heater. Route the other end of this line into a descaling reservoir

7.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.

8.Make sure all connections are "hand tight."

9.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.

10.Operate the circulating pump.

11.Make sure there are no leaks and the solution is flowing from the descaling reservoir through the heat exchanger and returning to the reservoir.

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