LAARS Mighty Therm LO-NOx PW (Sizes 500-1825) - Install and Operating Manual - Manual (Page 21)

Mighty Therm Lo-NOx Page 21
5. After the call for heat is satisfied the ignition
control closes the gas valves and operates the
blower for a thirty (30) second post purge cycle.
This clears the combustion chamber of
combustion products.
The ignition is attempted one time. If ignition is
not successful, the control shuts down and “locks
out.” It remains in the lockout condition until the
lockout reset button on the ignition control is reset.
6.2 Electrical Components
This section describes guidelines for checking
the operation of electrical components installed on the
heater. Refer to the wiring diagram for correct
connection locations.
6.2.1 General Troubleshooting
This section describes guidelines for checking
the electrical components of the heater. Experience
has shown that most complaints about heaters failing
to fire have nothing to do with the heater itself.
Usually, one of the protective switches in the heater
system has shut down operation.
Any of the following can prevent proper
operation. Check these items first:
1. Be sure the heater has been properly installed
(see Section 2 and 3).
2. Make sure the pump is not airlocked, clogged or
otherwise inoperative.
3. Make sure the gas valve is on and there is
sufficient gas pressure in the line. All external
gas valves must be open.
Caution
The ignition control and igniter operate on
115VAC power. Keep this in mind while
servicing the heater, and take care to avoid
electrical shock.
4. Verify that the electrical circuit serving the
heater is ON.
5. Make sure the toggle switch on the right side of
the heater is ON.
6. Check the fuse inside the black, twist-lock fuse
holder. If it is burned, replace it.
7. With the power off inspect all electrical connec-
tions and wiring. Finding a loose connection or
charred wire can save a lot of time and money.
8. Make sure the temperature controller is set high
enough to call for heat.
9. Make sure none of the manual reset controls, i.e.,
low water cutoff, high limit, etc., have tripped.
Reset any tripped switches.
If the pump is circulating water and the
foregoing items check out okay, the trouble may be in
the heater control system.
IMPORTANT: Disconnect power to the heater
before removing or replacing any component or wire
connection. If the power is not disconnected, “jumping”
the gas valve or accidentally grounding the wire harness
or component terminals to the heater frame or jacket
could cause the ignition control fuse to blow.
6.2.2 Electrical Troubleshooting
Troubleshooting procedures should only be
performed by professional service technicians
qualified in heater maintenance.
Some electrical components are wired in
parallel, so it is necessary to troubleshoot in the order
that they appear on the wiring diagram or the
troubleshooting flow chart (see Figure 21).
The following steps should be used when
troubleshooting the heater:
1. Remove the control panel cover of heater.
2. Turn the manual gas valve on the heater off.
3. If the heater has locked out turn the toggle
switch off for 5 seconds then back on to reset the
heater.
4. Use the troubleshooting flow chart (see Figure
21) to determine what components and wiring
should be tested first.
5. Test each component by checking for 24 VAC or
115 VAC entering and exiting the device. If
there is voltage entering the safety device, but
none leaving then there is an open circuit and it
must be determined why it is open. When testing
components between “MV ” of the ignition
control and the gas valve install a meter and let
the heater cycle through one complete sequence
of operation. During the sequence of operation
these safeties will only be energized for the
seven second trial for ignition.
6. Turn the manual gas valve of the heater on and
fire the heater.
Caution
Label all wires prior to disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation. Verify
proper operation after servicing.