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Main Burners; Vent Assembly / Heat Exchanger; Mineral Scale Build-Up; 1Descaling Heat Exchanger - Bosch 330-PN-N Installation Manual

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24 | Maintenance and service
Cleaning pilot assembly
Shut off gas supply to the heater using installer supplied
manual gas shutoff. Locate pilot gas tubing mounted in the
center of the burner assembly. At the base of the pilot gas
tubing there is a retaining clip. Release pilot gas tubing from
this clip. Push upwards on other end of pilot gas tubing to
release it from burner mount. Remove brass hex headed pilot
orifice from gas valve (located near base of pilot gas tubing).
Soak orifice and pilot gas tubing in carburetor cleaner for 30
minutes. Dry off and reinsert orifice in gas valve. If heater is an
LP unit, replace orifice. Reinstall the pilot gas tubing following
removal instructions in reverse. Open gas supply and return
heater to service.
▶ Do not ream or poke orifice as it will
enlarge orifice opening.

Main 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.

Vent assembly / heat exchanger

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 and/or heat
exchanger fins. 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.

Mineral scale build-up

The 330 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.
6.6.1 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.
4. Drain water from the unit's heat exchanger by disconnecting
inlet and outlet water connections
6 720 644 951 (2014/11)
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.
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.
330 PN



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