LAARS Mighty Therm LO-NOx PW (Sizes 500-1825) - Install and Operating Manual - Manual (Page 15)

Mighty Therm Lo-NOx Page 15
Figure 16. Two Temperature Hot Water Supply System with Vertical Tank.
during idle periods as well as when there is a demand
for hot water. It is recommended for general purpose
water supply including shower and bathing
applications. Water at 180°F is available directly from
the tank.
WARNING
Hot water can scald! Hot water can produce
third degree burns in 6 seconds at 140°F
(60°C) and in 30 seconds at 130°F (54°C).
SECTION 4.
Operating Instructions
4.1 Controls - General
(See Figures 17 and 18)
4.1.1 Electronic Ignition Control
This is a proved hot surface ignition control. It
combines a hot surface igniter and a flame sensor.
Upon a call for heat, the igniter is energized from a
nominal 120 VAC and is proven to be capable of
ignition. The gas valve(s) is then powered with 24
VAC establishing the flame at the burner(s). The
control then switches to the sensing mode to monitor
the flame presence. The unit performs its own safety
check during trial for ignition period and if the flame
is not established, the control interrupts the power to
the main gas valve(s) and goes into lockout.
4.1.2 Hot Surface Igniter
This is a 120 VAC, silicon carbide igniter.
During ignition cycle the igniter will glow for a few
seconds until reaching the proper ignition temperature
to ignite the gas at the burner ports.
4.1.3 Combustion Air Pressure Switch
The diaphragm type air pressure switch is
provided to prove the combustion air flow required for
proper combustion. Tube connection is attached to the
positive barbed end.
4.1.4 Operating Controls
Single or two-stage aquastats are provided in
models PH and PW heaters to control the desired
service water temperature. The temperature sensing
bulb is located either in the boiler inlet or outlet
header.
Legend
Check Valve
Tempering Valve
Venturi (Suction) Tee
Throttling Valves / Service Valves