LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 20)

LAARS Heating Systems
Page 20
hot water in the application.
After a setting has been chosen for the tank
temperature control, set the heater temperature control
10°F (6°C) higher. The heater’s temperature control
senses the inlet water temperature to the heater. The
heater’s manual reset high limit (and automatic reset
high limit, if applicable) senses heater outlet
temperature.
If the unit is equipped with an automatic reset
high limit, set the automatic reset high limit 20°F
(11°C) above the outlet temperature to avoid nuisance
lockouts. Set the manual reset high limit 5°F (3°C)
above the automatic reset high limit.
For units that only have a manual reset high limit
(no automatic reset high limit), set the manual reset
high limit 20°F (11°C) above the outlet temperature to
avoid nuisance lockouts.
Example, Imperial units: If the tank temperature
is set to 140°F, set the heater’s temperature control to
150°F (140°F + 10°F). Further, if the temperature rise
through the heater is 25°F, the outlet temperature will
be 175°F (150°F + 25°F). Therefore, set the automatic
reset high limit to 195°F (170°F + 20°F), and the
manual reset high limit to 200°F (195°F + 5°F).
Example, Metric units: If the tank temperature is
set to 60°C, set the heater’s temperature control to
66°C (60°C + 6°C). Further, if the temperature rise
through the heater is 15°C, the outlet temperature will
be 81°C (66°C + 15°C). Therefore, set the automatic
reset high limit to 92°C (81°C + 11°C), and the
manual reset high limit to 95°C (92°C + 3°C).
3.3.2. Internal Water Heater Temperature
Control:
When an external control is not used, the
circulator between the heater and the storage tank must
run continuously, so that the heater’s temperature
control can detect and control the water temperature in
the storage tank. The water heater’s temperature
control is adjusted to its lowest temperature position
(130°F, 54°C) when shipped from the factory. This is
the preferred starting point for setting the temperature
control.
If the unit is equipped with an automatic reset
high limit, set the automatic reset high limit 20°F
(11°C) above the outlet temperature to avoid nuisance
lockouts. Set the manual reset high limit 5°F (3°C)
above the automatic reset high limit.
For units that only have a manual reset high limit
(no automatic reset high limit), set the manual reset
high limit 20°F (11°C) above the outlet temperature to
avoid nuisance lockouts.
Example, Imperial units: If the heater’s
temperature control is set to 130°F, and the
temperature rise through the heater is 25°F, the outlet
temperature will be 155°F (130°F + 25°F). Set the
automatic reset high limit to 175°F (155°F + 20°F) and
set the manual reset high limit to 180°F (175°F + 5°F).
Figure 28. Temperature controls.
7. Turn manual gas valve on.
8. Reset all safety devices (some units have manual
resets on hi-limit switch, low water cutoff, etc.).
9. Set temperature control to desired setting.
10. Replace control access panel.
11. Turn electric power to the heater on.
12. If the heater will not operate:
a. Turn gas to heater off following the
instructions found on the inside of the heater
and call a qualified service technician or gas
supplier.
b. Turn main electrical switch off.
c. Close all manual gas valves.
3.3 Setting the Temperature Controls
The hi-limit switch is factory set, and should not
be adjusted above the factory setting.
WARNING
Adjusting the temperature control past the
recommended setting can result in a scalding injury.
Hot water can produce third degree burns in 6
seconds at 140°F (60°C) and in 30 seconds at
130°F (54°C).
3.3.1. Remote Water Heater Temperature
Control:
The water heater can be used with a field-
supplied tank aquastat, sequencing control, or other
temperature control device, which will call the unit for
heat when the temperature goes below the controller’s
setpoint. For the most efficient setting, set the tank
temperature at the lowest possible setting for adequate