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Absence of voltage at point 6 indicates that the
Flex Temp control is not calling for heat. Be sure that
knobs are set to call for heat as indicated earlier and as
described in the Operating Instructions section of this
manual. Verify that the thermistor sensor wires are not
severed or shorted. Check wiring connections by
removing the temperature control through the front of
the bezel. If the control is properly set and all wiring
and connections are correct, replace the Flex Temp
control.
4E-2g. Venturi Pressure Switch
Touch the voltmeter probe to point 7, which is
the terminal of the venturi pressure switch having a
purple wire connected to it. If there is no voltage at
point 7, the venturi pressure switch is open, indicating
inadequate flow through the combustion system. The
venturi pressure switch is a differential type switch
which is activated by the pressure difference created
when air flows through the venturi. When the
combustion blower is not operating, the venturi
pressure switch must be open and voltage will not be
present. See following sections on ignition control
"lockout" and combustion blower operation for
possible remedies.
Check for blockage at the combustion air inlet, a
dirty air filter or blockage at the vent exhaust or in the
vent. In improperly installed vent may trap condensate
water, for example, restricting flow. If there is no
obvious problem, analyze venturi operation as outlined
in a later section of this manual. If flow is normal,
replace the Venturi pressure switch.
4E-2h. Ignition Control
There will be voltage at point 8, which is the
“MVP” terminal of the ignition control, only when
there is an attempt to ignite the burner or when the
ignition control’s flame sensing system has determined
that it is OK to allow burner operation. Even if voltage
has been confirmed at point 7, the “trial for ignition”
sequence is imposed by the ignition control. This
sequence consists of a 15 second period of pre-purge
blower operation, a 20 second period for heatup of the
igniter and a 7 second trial for ignition, during which
there is voltage at point 8. If satisfactory ignition is not
achieved, the igniter is turned off and the blower is
operated for a 45 second post-purge. The system may
go through this cycle as many as three times, but
thereafter it is “locked out” by the ignition control.
Additional attempts will be made only if the call for
heat is interrupted by turning off electrical power or
setting the Flex Temp control to “Off”.
To trouble shoot the ignition control, connect the
voltmeter probe at point 8 and set the Flex Temp
control to call for heat. Observe that the normal
sequence takes place by noting blower operation, the
glow of the igniter through the combustion chamber
sight glass and then voltage at point 8. If the blower
4E-2c. Fireman Switch and External
Interlocks
Probe for voltage at point 3, the other connection
of the terminal block, which has a white wire
connected to it. 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.
4E-2d. Limit Switches
Probe for voltage at point 4, which is the water
pressure switch terminal with the white wire connected
to it. This switch is mounted on the end of a copper
tube and is about 2” in diameter. Absence of voltage at
this point indicates that 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. Water flow
deficiency may be due to obvious problems such as a
defective pump or blocked water filter. Alternatively, it
may be due to overfiring, or to a problem with the
water piping or the heater's internal bypass control.
Overfiring 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 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 fitting, 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 flow
deficiency, the most common one being a blocked water
filter. It may be due to causes cited in the previous
paragraph, however, and sometimes is due to blockage
of the copper tube or mis-adjustment of the switch.
Investigate thoroughly, referring to the earlier section on
“Adjustment of Pressure Switch”. If there is no problem
with the pool system or pressure switch adjustment,
replace the pressure switch.
4E-2f. Temperature Control
Probe for voltage at point 6, which is the terminal
of the venturi pressure switch having a yellow & black
wire connected to it. This is the switch mounted on the
frame above the blower between the vent diffuser and
the venturi tailpipe. It is about 4” in diameter.