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Page 24
Figure 32. Wiring diagram with test points.
pressure switch terminal with the white wire connected
to it. This switch is mounted on the end of a cop per
tube and is about 2" in diameter. Absence of voltage
at this point indicates that one of the limit switch es
is open. This is normally due to excessive water
temperature, which should be thoroughly investigated
before re place ment of limit switches. Water fl ow
defi ciency may be due to obvious problems such as a
defective pump or blocked water fi lter. Al ter na tive ly,
it may be due to overfi ring, or to a problem with the
water piping or the heater's internal bypass control.
Overfi ring might be a result of an incorrect gas orifi ce
or supply of propane gas to a heater intended for
natural gas. If there are no such fundamental problems,
identify which of the switches is open by temporarily
connecting a jumper wire across its terminals. Replace
a defective limit switch. Limit switch access is through
the side cover panel on the side of the heater to which
water pipes are connected.
Note that the limit switches have different
trip points, and it is important that replacements are
correct. The 150°F switch has a red dot on the side of
the brass fi tting, and must be installed closest to the
combustion chamber. The 135°F switch has no dot and
must be installed in the tapping closest to the water
piping connections.
4E-2e. Water Pressure Switch
Touch the voltage probe to point 5, which is the
other terminal of the water pressure switch having a
black wire is connected to it.
If there is no voltage, the pressure switch contacts
are open. This is almost always due to a water fl ow
defi ciency, the most common one being a blocked water
fi lter. It may be due to causes cited in the previous
para graph, however, and sometimes is due to blockage
of the copper tube or mis-ad just ment of the switch.
Investigate thoroughly, referring to the earlier section on
D
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