LAARS Mighty-Stack TL00-199 - Installation, Operation and Maintenance Instructions - Manual (Page 18)

LAARS HEATING SYSTEMS Page 18
3. There is an aquastat mounted near the bottom of
the tank. Eventually the water temperature at the
aquastat drops below the set point, and the
aquastat calls for heat.
4. When the aquastat calls for heat, the tank
circulator starts. (Notice that this happens before
the burner lights.) The water circulates through
the tank, and through the heater.
5. The pilot and main burners will then light, but
only if these conditions are satisfied:
• Aquastat closed – indicates the tank
temperature is below the set-point.
• High limit switch closed – indicates the water
temperature in the heater is below the high
limit set-point.
If all of these conditions are satisfied, the inducer
motor relay turns on the inducer fan.
6. The pressure switch closes, indicating that the
inducer fan is running. The pressure switch sends
24 volts to the flame rollout switch. In normal
conditions, the flame rollout switch is closed.
7. There is no continuously-burning pilot in this
unit. The pilot is lit each time the control system
calls for heat. At the start of the lighting process,
the gas valve/controller opens and the igniter
element glows. This lights the pilot flame.
8. The pilot flame produces a small electrical
current which is detected by the gas valve/
controller. Once the gas valve/controller detects
this current, the main burners light.
9. The main burners continue to run until the tank
aquastat reaches the set-point temperature. Then
the gas valve closes, and the draft inducer turns
off. After a short time delay, the pump turns off.
10. When the tank temperature at the aquastat falls
below the set-point, the cycle repeats.
3E. Cleaning the Pilot and Main Burners
This unit should not require cleaning very often.
If cleaning is necessary, the unit is designed so the
burners may be removed easily.
1. Turn off the gas at the manual gas valve.
2. On the front of the unit, a face plate covers the
ends of the burners. Undo the four thumbscrews
and remove the face plate.
3. Disconnect the white Molex ® connector which
runs to the gas valve.
4. Disconnect the gas manifold.
5. The burners are mounted on a sliding tray. Pull
out this tray to reach the burners.
6. The pilot is mounted on the right side of the
assembly. Clean the pilot if the flame appears to
be yellow or smoky, if the gas flow seems to be
restricted, or if the pilot takes a long time to
light. If you see signs of fouling, clean the
assembly very gently using a bristle brush.
NOTE: Be very careful not to clean the tip of
the hot surface unit. (This is located in the center of
the pilot assembly.) This part is very delicate.
7. In order to clean the pilot orifice itself, you must
remove the part from the bracket. Gently clean
out the center of the orifice using a small wire.
8. Check the main burners. They should be cleaned
if they are dirty, or if the flames are yellow or
smoky. Brush off the top of each burner using a
bristle brush.
9. An orifice is located at the end of each burner.
To clean one of these parts, you must remove it.
Gently clean out the center of the orifice using a
small wire.
10. Once the burners have been pulled out, you can
reach up and clean the underside of the heat
exchanger.
11. Reassemble the burners and the pilot.
Reassemble the gas manifold, and reconnect the
pilot connector. Replace the cover plate.
12. Turn on the gas valve. Check for gas leaks
before you use the water heater.
Figure 15. Pilot Assembly.