3
6 720 607 026
Principle of Operation:
When a hot water faucet is opened, the water flow through
the heater causes the gas valve to open. At the same time
the hydro-generator activates the electronics which sends
a spark to the pilot. The flame sensor confirms the pilot has
been lighted and allows the first two burners to come on.
The flame sensor confirms correct activation and all burners
come on. The pilot goes off. The heat exchanger coils absorb
the heat generated by the burners and transfer heat to the
water. When the hot water faucet is shut off, the gas valve
automatically closes and the burners turn off. Your hot water
faucet is an ignition key to activate the water heater, giving
you control over your hot water energy use. Every time you
turn off your hot water faucet, the energy consumption of
your hot water returns to zero.
FEATURES
- Electronic Pilot Ignition driven by hydro-generator
- High Quality Materials for Long Working Life.
- Copper heating coils for endless supply of hot water.
- Burner output proportional to hot water flow demand for
maximum energy efficiency.
- Safety flame sensor at pilot burner.
- Automatic overheating protection shut-off sensor.
- Flue gas safety device.
- Stainless steel burners with stabilized blue flame.
- Built-in corrosion resistant draft diverter.
- Compact space saver: mounts on a wall with two hooks.
- Easily removable one-piece cover.
- Easy one person installation.
- Adjustable water flow restrictor to ensure that water flow
demand will not exceed the heating capacity of the heater.
- On/Off Switch to activate system.
- Red LED indicator flashes with low water pressure.
- Green LED indicator main burner operation.
BOSCH is constantly improving our products, therefore
specifications are subject to change without prior notice.
425 HN LP and 425 HN NG Specifications
Gas Input max.: 117,000 Btu/hr
min.: 28,000 Btu/hr
Water Connection
½
” Thread fitting NPT
H x W x D 29 3/4” x 18 1/4” x 8 3/4"
Vent 5”
Gas Connection 1/2” NPT thread
Min. Water Pressure 18 Psi at 4 GPM
Max. Water Pressure 150 Psi
Shipping Weight 43 LB
Net Weight 40 LB
1.8 GPM at 90° rise
3.7 GPM at 45° rise
Min. Water Flow 1/2 gal/min
LP GAS Supply Pressure
(before 425 HN regulator)
min. 11” W.C.
max.
14” W.C.*
Required LP GAS Pressure at inlet
tap while 425 HN is operating:
10.5” W.C.
LP GAS Burner Manifold pressure while 425 HN is
operating at maximum input:
9.0” W.C.
Natural Gas Supply Pressure
min.: 7” W.C.
(before 425 HN regulator)
max.: 14” W.C.*
Required Natural Gas Pressure at inlet
tap while 425 HN is operating:
5.7” W.C.
Natural Gas Burner Manifold Pressure while 425 HN is
operating at maximum input:
4.2” W.C.
* Inlet gas pressure before 425 HN regulator must not exceed
this value. Pressure may need to be adjusted for high
altitudes, see page 7.
UNPACKING THE 425 HN HEATER
This heater is packed securely. The box includes one water connection fitting, a control knob with collar, a gas pressure
regulator, a pressure relief valve, an incandescent particle tray, two hooks for hanging the heater, this manual and a
warranty registration card.
Do not lose this manual, as there is a charge for replacement.
Please complete and return
the enclosed warranty registration card.
