Safety Controls/Air Flow Switch (Afs); Water Pressure Switch; High Limits (Safety Device) - Pentair MT125 Installation And User Manual

Section 2. Operations
44
SAFETY CONTROLS
AIR FLOW SWITCH (AFS)
The air flow switch, (see Figure 42), is a safety device used to insure that the combustion air
blower (fan) is operating and has been designed to monitor the vacuum (negative) pressure
within the blower housing. The air flow switch is factory set and is connected upstream of
the ignition module. The ignition module does not operate unless the air pressure switch and
all safety switches are closed.

WATER PRESSURE SWITCH

Hazardous pressure. Do not bypass the
Water Pressure Switch or render inoperable.
The water pressure switch, see Figure 44. If the water flow is restricted, the water
pressure switch may prevent the burner from firing and cause the "Service System"
light to go on. If the light remains on after the filter has been serviced, have a qualified
service technician check the system.
For deck-level heater installations, the Water Pressure Switch is factory
set at (20.6 kPa) 3.00 psi. NOTE: See, "Below Pool Level Installation"
instructions on page 14. If the pressure switch is 3 M (1 ft.) below or above
the pool water level, reset the switch so that it is open when the pump is off and
closed when the pump is running. Turn the star-wheel on the switch clockwise
( ) to raise setting (heater below the pool) and counterclockwise
( ) to lower the setting (heater above the pool – see Figure 44. Test the switch
after resetting.
NOTICE: When the heater is mounted more than 1.5M
(5 ft.) above or 1.2M (4 ft.) below the deck level, a
Pressure Switch is no longer adequate. A Flow Switch
must be installed instead.
NOTICE: Heater operation with incorrect Pressure
Switch setting may cause operation with no water flow.
Operation of the heater without sufficient water flow
may severely damage it.
HIGH LIMITS
A "High Limit", is a safety device that opens the
electrical circuit and shuts off the heater based on a water
temperature set point within the "High Limit Device".
The heater contains two (2) high limit devices which are
located on the main inlet / outlet header.
MASTERTEMP 125 Pool and Spa Heater Installation and User's Guide
WARNING
Turn star wheel clockwise to raise
pressure set point if pressure switch is
more than 4 feet (1.2M) below water level
A reference scale is on
the back of pressure switch
Turn star wheel counterclockwise to lower
pressure set point if pressure switch is more
than 5 feet (1.5M) above water level
Figure 42.
Air Flow Switch
Water
Pressure
Switch
Figure 43.
Water Pressure Switch
Star Wheel
Figure 44.
460906 Rev. D 8/2020