Maintenance And Service; Maintenance Intervals; Water Valve - Bosch 520-HN -L Manual

24 | Maintenance and service

▶ Empty the appliance of all water.
1
2
Fig. 23 Draining
[1] Retaining clip
[2] Threaded bushing
[3] Filter
For increased safety shut off the appliance from the main water
supply if you are staying away from home for a considerable
time.
WARNING:
▶ To prevent any freeze damage,
introduce short bursts of compressed
air (20-40psi) through the outlet water
connection to remove the residual water
in the horizontal pipes and water valve.
6 Maintenance and service
6.1

Maintenance intervals

WARNING:
▶ Failure to perform recommended
maintenance may result in complete
failure of the unit over time.
The warranty does not cover failures
due to improper or insufficient
maintenance.
The 520 HN requires periodic maintenance. The time
maintenance intervals below should keep the unit operating for
many years.
Every year
▶ Inspect inlet water filter screen ( 6.2)
▶ Inspect pilot assembly and flame ( 6.3)
▶ Inspect burner assembly ( 6.4)
6 720 644 942 (2014/11)
3
6720608032-12.1Av
Every 2 years
▶ Inspect heat exchanger fins for soot, debris or blockage.
Clean if necessary (5.5)
▶ Clean and Lubricate water valve ( 6.2)
Every 3 to 5 years
▶ Rebuild water valve with parts kit (part# WVKITCT) ( 6.2)
▶ Clean pilot assembly and clean or replace orifice ( 6.3)
6.2

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.bosch-
climate.us. 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. 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. 27, num. 4). Remove and inspect the venturi
and clean if necessary. (see Fig. 27, 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.bosch-climate.us. Failure to rebuild the water
520 HN