20 | Operation instructions
Plumbing connections and pressure relief valve
shown with optional Webstone service valves
4.10 Recirculation application
Since recirculation through the heater is not permissible, the
following drawing is provided to outline a proper recirculation
application using the BOSCH PRO water heater with an Ariston
minitank. This schematic is for illustration only and must not be
used for actual installation without appropriate engineering
and technical advice from a professional properly licensed in
locality where the installation is made.
 Full port isolation valve
 Check valve
 Expansion tank
6 720 644 951 (2014/11)
The use of a small electric mini-tank (4-6 gallon size) should be
used for this application and designed so the pump will
circulate the water through the mini-tank and the building's hot
water return loop only. A timed or thermostatically controlled
operation of the pump is commonly done. The 330 PN should
be plumbed in line before the mini-tank water heater. Contact
Bosch Water Heating if further instruction is needed.
For your safety read before operating your
▶ If you do not follow these instructions
exactly, a fire or explosion may result
causing property damage, personal
injury or loss of life.
Upon initial installation, existence of air in
the gas supply line and in the water line may
cause some ignition delay. In that case,
repeat the ignition process until all the air
has been purged.
A. This appliance employs a piezo-igniter to light the pilot
burner. When lighting the pilot, follow these instructions
B. What to do if you smell gas.
WHAT TO DO IF YOU SMELL GAS
▶ Close gas valve. Open windows.
▶ Do not try to light any appliance.
▶ Do not touch any electric switch; do not use any phone in
▶ Immediately call your gas supplier from a neighbors phone.
Follow the gas supplier's instructions.
▶ If you cannot reach your gas supplier, call the fire
C. Use only your hand to push in the gas control buttons. Never
use tools. If a button will not push in, check to make sure the
buttons are being pushed in the proper sequence. Follow these
instructions exactly. If control button(s) are jammed, close the
heater's individual manual shutoff valve and call a qualified
service technician. Forced or attempted repair may result in a
fire or explosion.
D. Do not use this appliance if any part has been under water.
Immediately call a qualified service technician to inspect the