LX and LT Low NOx Pool/Spa Heater Page 41
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 covers on the side of
the heater to which water pipes are connected.
Remove the limit switch covers from the header and
gently remove the switches from the wells.
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 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.
Leave one meter lead in place at test point 1.
Move the other meter lead to the terminal connection
on the 150° switch (test point 13) that is connected
back to the controller. The voltmeter should read 20-28
Volts. No voltage here means that the ten-pin wire
harness is bad and should be replaced. If voltage is
detected at this point move the lead to the other
terminal of the switch (test point 14). If the voltmeter
does not show voltage then the 150° limit is bad and
should be replaced. If the meter reads 20-28 Volts,
move the lead to the terminal of the 135° limit that is
connected to the wire that jumps between the two limit
switches (test point 15). No voltage here means that
the wire assembly is bad and needs to be replaced. 20-
28 Volts shows that the wire between the two limits is
making a good connection. Now move the lead to the
other connection terminal on the 135° limit (test point
16). No voltage at this point indicates that the limit
switch has failed and needs to be replaced. Voltage
here would show that the limit is good and that the ten-
pin wire harness may have a bad connection. Replace
the wire harness if necessary.
10.5.3.5 Fusible Link / Exhaust
Temperature Limit Switch Circuit
Since the exhaust temperature limit switch is not
easily accessible, you can check the voltage between
test point 1 and the two legs of the circuit at the back
of the controller (see test points 17 and 18 in Figure
39).
Leaving the black lead of the meter on test point
1, check the voltage at test point 17, where the white
wire from the fusible link enters the ten-pin connector
on the back of the controller. If there is not 20-28
Volts at this point, either the controller or the ten-pin
wire harness is faulty and must be replaced. If 20-28
Volts is detected at this point, then move the red lead
of the meter to test point 18 where the white wire
from the manual reset high limit switch enters the ten-
pin connector. If 20-28 Volts is detected at this point,
the devices in this circuit are closed and the circuit is
working properly.
If there is no voltage, either the fusible link or the
contacts of the manual reset switch are open. To
determine which device is causing the fault, check the
fusible link first.
Leave one lead of the meter at test point 1.
Move the other lead of the meter to the contact on the
fusible link where the wire is connected back to the
controller, (test point 19). Voltage to this point means
that the wire harness between the controller and the
water fusible link is good. If there is no voltage at test
point 19, look for a loose connection or replace the
ten-pin wire harness. If there is voltage at test point 19
then move the lead to the contact on the other side of
the fusible link (test point 20). No voltage here means
that the fusible link is open. 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 tempera-
tures are almost always due to flashback conditions
caused by a damaged burner, manifold pressure being
set too high or incorrect gas supply type. Check to be
sure that the type of gas being supplied to the heater
matches the designation on the rating plate. Thor-
oughly inspect the burners and orifices for damage.
Finally, check and adjust the manifold pressure if
necessary. Replace the fusible link. If test point 20
shows 20-28 Volts, then the top of the heater must be
removed to gain access to the manual reset exhaust
limit switch.
To check the manual reset switch leave one lead
of the meter at test point 1 and place the other lead on
the contact of the manual reset switch (test point 21)
that is connected to the wire leading to the fusible link.
If test point 21 does not show 20-28 Volts, then the
wire assembly between the fusible link and the manual
reset switch must be replaced. If 20-28 Volts is
detected, then move the lead to the other contact of
the manual reset switch (test point 22). Voltage here
means that the ten-pin connector wire harness is faulty
and must be replaced. If no voltage is detected, the
switch contacts have opened due to excessive exhaust
temperatures. This condition is usually caused by a
blocked exhaust vent. Be sure that the vent is clear of
all debris, then push the red button on the switch to
reset the circuit. If there is still no voltage detected,
the manual reset switch must be replaced.
10.5.3.6 Blower Pressure Switch Circuit
The blower must be operating during the test
procedure for the blower pressure switch. Start by
checking the voltage between test point 1 and the two
legs of this circuit at the back of the controller, (see
test points 23 and 24 in Figure 39).
Leaving the black lead of the meter on test point
1, check the voltage at test point 23, where the purple
wire from the blower pressure switch enters the ten-
pin connector on the back of the controller. If there is
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