Many of the questions customers ask regarding operation of
this unit can be answered by following the troubleshooting
steps as outlined below. Visit our web site at www.bosch-
climate.us for more detailed troubleshooting. For best results,
perform each step before proceeding to the next. The
suggested solutions may require that the cover be taken off.
(See chapter 4.4).
Pilot does not light
1. Verify gas supply is on at Natural Gas meter or Propane Tank.
Make sure all manual gas shut off valves are in the open
position. Have licensed gas technician confirm adequate gas
pressure at the inlet tap (chapter 4.9). If gas is not present,
verify manufacturer supplied Maxitrol regulator is in the upright
position. The arrow on the back of the regulator should point in
the same direction as gas flow.
2. If the unit was just installed or the gas lines have been
worked on, there may be air in the gas line. Centered in the
sparking position, hold down the gas control slide button while
hitting the pilot igniter button every few seconds. It may take
several minutes to bleed air out of the gas line.
3. Verify a spark is being thrown at pilot area while gas control
slide button, centered in the single flame position, is being
firmly depressed. Repeatedly push in pilot igniter button to
light the pilot. If no spark is present, verify proper wire
connection to the electrode.
4. Pilot assembly may be blocked. Clean or replace the pilot
orifice (chapter 6.3).
Pilot lights, but goes out when button is
1. When lighting pilot ensure the gas control slide button is fully
depressed and held down for at least 20 seconds after pilot is
2. 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.
3. Check all connections of the pilot safety circuit. The pilot
safety circuit consists of a thermocouple, overheat sensor
(ECO), flue gas sensor, safety spillage switch(models with
Powervents only) and the electromagnet (See parts diagram
for locations). Clean sensor connections with light sandpaper if
corrosion is evident. The electromagnet connection is 5mm nut
from the thermocouple which screws into a larger 17mm nut.
Tighten both nuts snugly but do not over tighten.
4. Pilot flame should be blue in color and completely engulfing
the tip of the thermocouple. If not, have a licensed gas
technician verify gas pressure is in accordance with
manufacturer's specifications (chapter 4.9) and clean or
replace the pilot orifice (chapter 6.3).
5. Have a licensed gas technician verify the proper operation of
the thermocouple by measuring the millivoltage from the
thermocouple lead to ground. The proper reading should be
24mVDC or greater. If the reading is lower, the thermocouple
may be defective. Call Bosch Water Heating for further
Pilot goes out during or after hot water use
1. Pilot outage during use typically results from the unit's safety
overheat/high limit sensors interrupting the pilot circuit. The
330 PN does not have a thermostat. If inlet water is preheated,
the unit will overheat, stopping the flow of gas. Plumb inlet with
a cold water line only.
2. Failure to vent properly by reducing pipe diameter, improper
use of elbows or not meeting required vent length are common
causes that deactivate the pilot safety circuit. Confirm venting
is in accordance with manufacturer's specifications (see
3. Confirm the combustion air requirements are being met in
accordance with manufacturer's specifications (see
chapter 4.6). Proper venting and combustion air will ensure a
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