Maintenance And Service - Bosch 520-HN-N User Instructions

5

Maintenance and service

5.1 Maintenance intervals
Failure
Warning:
recommended maintenance may result
in complete failure of the unit over time.
The warranty does not cover failures
due to improper
maintenance.
The 520 HN requires periodic maintenance. The time
maintenance intervals below should keep the unit
operating for many years.
Every year
B Inspect inlet water filter screen ( 5.2)
B Inspect pilot assembly and flame ( 5.3)
B Inspect burner assembly ( 5.4)
Every 2 years
B Inspect heat exchanger fins for soot, debris or block-
age. Clean if necessary (5.5)
B Clean and lubricate water valve ( 5.2)
Every 3 to 5 years
B Rebuild water valve with parts kit (part# WVKITCT)
( 5.2)
B Clean pilot assembly and clean or replace orifice
( 5.3)
5.2 Water valve
The water valve is the main control that tells the heater
to fire. If the periodic maintenance is neglected, more
costly damage may occur.
Inspecting inlet water filter screen
Shut off the installer supplied cold water shut-off valve
to the heater. If one is not installed, install before
proceeding. Open the nearest hot water tap to drain the
plumbing lines. Position a bucket under the heater's
water valve assembly to catch any water that may drain
from the heater. Remove the filter retaining clip located
at base of water valve (see Fig. 24). Remove the
bushing to access the cylindrical filter inside. Remove
filter, clean with water and inspect for damage. If the
filter is damaged, it must be replaced.
Lubricating the water valve
Service bulletins are available on our website at
www.boschpro.com. Shut off the installer supplied cold
water shut-off valve to the heater. If one is not installed,
install before proceeding. Open the nearest hot water
tap to drain the plumbing lines. Position a bucket under
the heater's water valve assembly to catch any water
6 720 644 942
to perform
or insufficient
that may drain from the heater. Disconnect the inlet
water pipe going to the back of the water valve.
Disconnect the water pipe leading out of water valve to
the heat exchanger. Do this by removing the retaining
clip on water valve assembly and pulling the pipe free
from the water valve. Loosen the two set screws
underneath the water valve where it connects to the gas
valve. If the set screws are seized, STOP and call
Bosch tech support before proceeding. Forcing and
breaking seized set screws may damage the water valve
and gas valve assemblies. Remove the water valve by
pulling it to the right. Separate the two halves of the
water valve by removing the five screws on the left side
of the water valve. Apply lithium or faucet & valve grease
to the pushrod and o-ring. (See Fig. 28, num. 4).
Remove and inspect the venturi and clean if necessary.
(see Fig 28, num. 23).
Rebuilding the water valve
Several parts within the water valve must be replaced
every 3 to 5 years depending on water quality and
usage. For more detailed instruction, bulletin CT-23 can
be found on our website at www.boschpro.com. Failure
to rebuild the water valve can result in decreased
performance or water leaks in the heater.
5.3 Pilot
Inspecting pilot
The pilot should burn with a clean sharp blue flame. The
flame should fully engulf the bend of the flame sensor. If
it does not, clean the pilot assembly using the
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.
Maintenance and service
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