Draining water from heater
If there is a risk of freezing, proceed as follows:
▶ Remove the retaining clip from threaded bushing (pos. 1).
▶ Remove threaded bushing (pos. 2) from water valve.
▶ Empty the appliance of all water.
Drain plug and filter location
 Retaining clip
 Threaded bushing
Maintenance and service
▶ 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
The 330 PN requires periodic maintenance. The below time
maintenance intervals should kept the unit operating for many
▶ Inspect inlet water filter screen ( 6.2)
▶ Inspect pilot assembly and flame ( 6.3)
▶ Inspect burner assembly ( 6.4)
Every 2 years
▶ Inspect heat exchanger fins for soot, debris or blockage.
Clean if necessary (5.5)
▶ Lubricate and clean water valve ( 6.2)
Every 3 to 5 years
▶ Rebuild water valve ( 6.2)
▶ Clean pilot assembly and clean or replace orifice ( 6.3)
The water valve is the main control that tells the heater to fire.
If the periodic maintenance is neglected, more costly damage
may occur over time.
Inspecting inlet water filter screen
Shut off the installer supplied cold water isolation 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 pin located at base of water valve (see Fig. 24).
Remove the threaded bushing to access the cylindrical filter
inside. Remove filter, clean with water and inspect for damage.
If the filter is at all damaged, it should be replaced.
Lubricating the water valve
A more detailed instruction is available on our website at
www.bosch-climate.us. Shut off the installer supplied cold
water isolation 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
pin on water valve assembly and pulling the pipe free from the
water valve. Loosen the two set screws at the bottom of 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 snapping seized set screws may cause
irrevocable damage to 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).
Inspect the venturi and clean if necessary. (see Fig 27).
Rebuilding the water valve
Several parts within the water valve should be replaced every 3
to 5 years depending on water quality and usage. The parts list
and instructions can be found on our website at www.bosch-
climate.us. Failure to rebuild the water valve can result in
decreased performance or damage to the heater.
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.
Maintenance and service | 23
6 720 644 951 (2014/11)