Pentair 300, 250 Safety Controls, AIR Pressure FAN Switch, Water Pressure Switch

Basic Operation		21
SAFETY CONTROLS
AIR PRESSURE (FAN) SWITCH
The air pressure switch is a safety device used to insure
that the blower (fan) is operating and has been
designed to monitor the vacuum (negative) pressure
within the blower housing. The air pressures switch
is factory set and is in the ignition module circuit—
the ignition module does not operate unless the air
pressure switch and all safety switches are closed.
NOTE
Some models of MiniMax NT Low NOx heaters,
manufactured before 10-15-01, used both a HIGH
and LOW air pressure switch.	Figure 18.	AIR PRESSURE SWITCH
WATER PRESSURE SWITCH

The water pressure safety switch closes when there is a sufficient flow of water to the heat exchanger to safely operate the heater. The switch operation must be verified during initial operation of the heater after installation—the switch is set at 1 PSIG and the switch contacts must not be closed in the absence of water flow. NOTE: See, Below Pool Level Installation instructions on page 13. The switch may remain closed with no water flow if there is more than a 3 ft. elevation difference between the heater (heat exchanger) and the pool water line—if this is the case, the water pressure switch must be reset to maintain open switch contacts with no water flow.

NOTE

Figure 19.

Adjustment Knob

Typical Water Pressure Switch

If the pool is more than one floor above or one floor below the heater, the pressure switch may have to be replaced with a flow switch.

LOW GAS PRESSURE SWITCH (LOW NOx Versions Only)

The MiniMax NT Low NOx heater uses a low gas supply pressure switch, ahead of the gas valve, to prevent operation of the heater when the gas supply pressure is below the minimum required for proper operation of the burners. The switch is factory set. In the event that the switch does not close and prevents the firing of the heater, the cause of the low gas supply pressure must be corrected. Typical causes are undersized supply piping, undersized gas meter or low gas regulator setting (gas supply regulator and gas meter problems are typically corrected by your local gas company).

Figure 20.

Low Gas Pressure Switch

Rev. C 11-1-01 P/N 471593