Bosch Model GWH 425 - Manual (Page 22)

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Troubleshooting
the way clockwise, the flow rate should be close to
2gpm, filling the jug in 15 seconds. With the
temperature adjustment knob set all the way
counterclockwise, the flow rate should be close to
4gpm, filling the jug in 7 seconds. If the flow rate is not
adequate, inspect and clean the inlet filter screen (see
chapter 5.2).
2. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads,
faucet aerators and whole house filters are clear of
debris. Restrictions in the water path can slow water
flow through the heat exchanger causing it to boil and
make noise.
3. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing the water to boil resulting in noise
and overheating. Instructions for descaling the heat
exchanger are available at www.boschpro.com.
6.12 Burners do not operate cleanly;
yellow flames when operating
1. Verify gas type indicated in rating sticker located on
right-hand side of cover, coincides with the gas type
you are using. NG is a natural gas unit and LP is for
liquid propane.
2. Gas pressure may be inadequate resulting in
improper combustion. Ensure gas pressure is in
accordance with manufacturer's specifications (see
chapter 3.6). A gas pressure reading is needed to
proceed further. Contact your original installer or a
licensed gas technician to obtain this reading.
3. For proper combustion at high elevations the inlet
gas pressure should be set at installation to the value
shown in table 3 (while operating at maximum BTU). A
gas pressure reading is needed to proceed further.
Contact your original installer or a licensed gas
technician to obtain this reading.
4. Ventilation is not adequate. Ensure adequate
combustion air is being supplied to the unit in
accordance with manufacturer's specifications (see
chapter 3.6).
5. Make sure the water heater is vented properly. Check
for proper draft and ensure venting is in accordance
with manufacturer's specifications (see chapter 3.7).
6. The water heater has burners much like a furnace. It
is essential that they remain clean and are supplied with
adequate air for combustion. If the flames burn yellow or
orange, it is strongly recommended that the burners be
removed from the unit and cleaned. Once the burners
are removed, the fins in the top of the heat exchanger
can be accessed and brushed or vacuumed clean.
Instructions to remove burners are available at
www.boschpro.com.