Model LG Pool and Spa Heater
Page 31
If no voltage is detected at test point 3, the wire
between the gas valve and the fusible link is broken.
Replace the wire.
If there is a minimum of 220mV at test point 3,
move the black meter lead to the other terminal of the
fusible link (test point 4).
If no voltage is detected at test point 4, the
fusible link has failed. This indicates higher than
normal temperatures in the component compartment
(vestibule). Normal component compartment tempera-
ture is well below 300
o
F. The fusible link is designed
to fail at temperatures above 305°F. Excessive tem-
perature might be due to a blocked flue or heat ex-
changer. Clean the heat exchanger and clear the flue
and vent of any restrictions. Sometimes the fusible
link fails due to flame roll-out. Flame roll-out may be
caused by delayed ignition or downdrafting in windy
areas. Thoroughly investigate the causes for flame
roll-out and correct the problem when replacing the
fusible link.
10.4.4
Fireman Switch and External
Interlocks
Check the voltage going to the external device.
Touch the black lead of the meter to the fireman
switch terminal strip where the white wire from the
fusible link is connected (test point 5). The meter
should read at least 220mV. If the voltage is less than
220mV, there may be a bad connection or wire
between the fusible link and the terminal strip. The
wire may need to be replaced. If voltage of 220mV or
more is detected at test point 5, move the black lead of
the meter to the fireman switch terminal strip connec-
tion where the white wire from the high limit is
connected (test point 6). The meter should read at least
220mV. If there is no voltage, the time clock switch or
other external interlock may be mis-adjusted, mis-
connected or defective. Correct this external problem.
10.4.5
Limit Switches
Since the limit switches are not easily accessible,
you can check the voltage going into the component
after the limit switches in the circuit. If voltage is
detected there, then the limit switches are closed and
are operational.
Check the voltage going to the water pressure
switch. Leave the red voltmeter lead in place at test
point 1. Touch the black lead of the meter to the
terminal of the water pressure switch where the white
wire is connected (test point 11).
If the voltage is less than 220mV, there may be a
bad connection, a partial short or a faulty sensor. If
there is no voltage, one of the limit switches is open.
This is normally due to excessive water temperature,
which should be thoroughly investigated before
replacement of limit switches. Excessive water
temperature may be caused by low water flow. Water
flow deficiency may be due to obvious problems such
as a defective pump or blocked water filter. Alterna-
tively, excessive water temperature may be due to
over-firing, or to a problem with the water piping or
the heater's internal bypass control. Over-firing might
be a result of an incorrect gas orifice 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. Limit switch
access is through the limit switch cover on the inlet/
outlet header. Remove the cover and retainer bracket
from the high limit switches and remove the limit
switches from the wells. Move the black lead of the
meter to the terminal on the 150°F limit switch (test
point 7) that is connected to the fireman switch
terminal block. Less than 220mV at this point means
that the wire between the terminal block and the limit
switch has a poor or broken connection or a partial
short. Replace the wire assembly. If at least 220mV is
detected at test point 7, then move the black lead of
the meter to the other terminal of the 150°F limit
switch (test point 8). Low or no voltage here means
that the limit is open and must be replaced.
If 220mV or more is detected at test point 8,
move the black lead of the meter to the terminal on the
135°F limit switch (test point 9) that is connected to
the 150°F limit switch. Less than 220mV at this point
means that the wire between the two limit switches has
a poor or broken connection or a partial short. Replace
the wire assembly. If at least 220mV is detected at test
point 9, then move the black lead of the meter to the
other terminal of the 135°F limit switch (test point
10). Low or no voltage here means that the limit is
open and must be replaced. If voltage is detected at
test point 10, move the black lead of the meter to the
terminal of the water pressure switch where the white
wire from the high limits is connected (test point 11).
Less than 220mV at this point indicates that the wire
connecting the high limits to the water pressure switch
is faulty or poorly connected. Correct the problem or
replace the wire.
Note:
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 top of the brass fitting, and must be
installed in the lower (horizontal) well in the
header. The 135°F switch has no dot and must
be installed in the upper (vertical) well in the
header.
