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valve can result in decreased performance or water leaks in the
heater.
6.3
Pilot
Inspecting pilot
The pilot should burn with a clean sharp blue flame. The flame
should fully engulf the tip of the thermocouple. If it does not,
clean the pilot assembly per procedure below.
Cleaning pilot assembly
Shut off gas supply to the heater using installer supplied gas
shutoff valve. Remove 2 screws mounting pilot burner to front
of burner assembly. Remove the filter screen at the base of the
pilot burner. Remove 8 mm brass hex head pilot orifice from
pilot electrovalve. If heater is a NG model, soak orifice and pilot
burner in carburetor cleaner for 30 minutes. Dry, blow out with
compressed air and reinstall orifice. If heater is an LP model,
replace orifice. Reinstall the pilot burner following removal
instructions in reverse. Open gas supply and return heater to
service.
CAUTION:
▶ Do not ream or poke orifice as it will
enlarge orifice opening.
6.4
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, dirty burners or 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 and refer to service
bulletin CT-13.
6.5
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.
6.6
Mineral scale build-up
The 520 HN, when operated at lower temperatures settings,
does not accumulate mineral build-up. If however, the heater is
used at higher temperature settings and the water has a high
mineral content, mineral deposits (scale) may form within the
heat exchanger and periodic descaling may be necessary. The
heat exchanger should be flushed with a descaling solution.
520 HN
6.6.1 Descaling heat exchanger
1. Shut off the water supply to the water heater using (installer
supplied) shut-off valve.
2.Open hot water taps to drain and relieve pressure from the
plumbing system.
3. Drain water from the unit by disconnecting inlet and outlet
water connections.
4. Connect the line (A) from the outlet of the circulating pump
(installer supplied) to the inlet water fitting on the water heater
5. 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.
6. 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.
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.
▶ Several hours may be necessary to flush the heater
thoroughly.
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 shut-off valve and
flush heater with clean water.
14. Shut cold water shut-off valve and reconnect hot water
supply to the water heater.
15. Open open water shut-off valves, and return the unit to
service.
Maintenance and service | 25
6 720 644 942 (2014/11)
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