P/N 475114 Rev. F 8/2020 MASTERTEMP 125 Pool and Spa Heater Installation and User’s Guide
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HEATER DESCRIPTION
Figure 10 shows a diagram of the heater and how it operates.
Precisely matched orice plates meter the air and gas into the mixer.
The blower draws the air and gas through the mixer and forces it
into the burner’s ame holder. A sealed heat exchanger surrounds
the ame holder, discharging exhaust gases out the ue.
50 mm (1.5 in - UK) PVC water piping connects directly to the
manifold/header on the heat exchanger using 50 mm (1.5 in - UK)
PVC slip unions provided with the heater. The outer manifold
remains cool; no heat sinks are required. A thermal regulator and an
internal bypass regulate the water ow through the heat exchanger
to maintain the correct outlet temperature. The heater operator
control panel board assembly is located on top of the heater.
SEQUENCE OF OPERATION
An electronic temperature sensing thermistor in the manifold adapter inlet controls the heater operation. When the inlet
water temperature drops below the temperature set on the operating control, the burner controller supplies power to
the combustion air blower through a series of safety interlocks. The interlocks consist of;
• the pressure switch (PS), which senses that the pump is running,
• the high limit switch (HLS), which opens if the heat exchanger outlet temperature goes above 55° C (131° F), and
• the air ow switch (AFS), which senses the pressure drop across the air metering orice,
• the automatic gas shut-off (AGS) switch, which opens if the heat exchanger outlet temperature goes above 60° C
(140° F).
• the inlet temperature control switch, which opens if the inlet temperature goes above 45° C (110° F).
• the stack ue sensor (SFS), which shuts down the heater if the ue gas temperature reaches 249° C (480° F).
The air ow switch (AFS) senses the pressure drop across the air metering orice. As soon as there is sufcient air ow,
the AFS closes, closing the circuit to the hot surface igniter (HSI), which ignites the fuel mixture. On a call for heat,
the blower and HSI are energized. In about 20 seconds, the gas valve opens and ignition occurs. The HSI then switches
to a sensing mode and monitors the ame. The heater is equipped with a digital operating control that enables the user
to pre-set the desired pool and spa water temperatures. The control enables the user to select between pool and spa
heating, and features a digital display that indicates the water temperature.
Section 1. Installation
Gas
Air
Mixer
Blower
Inlet
(Cold
Water)
Exhaust
Heating Coils
Outlet
(Mixed
Water)
Burner
Figure 1.
Section 1. Installation
This product must be installed and serviced by a professional service technician, qualified in pool heater installation.
THE MASTERTEMP HEATER IS INTENDED FOR INSTALLATION WITH A METERED GAS PRESSURE
REGULATOR.
Pentair strongly recommends that all vents, pipes and exhaust systems be initially and periodically tested for proper
operation. This testing can be accomplished by using a hand-held carbon monoxide meter and/or by consulting with a
gas professional.
Pool heaters must be used in conjunction with carbon monoxide detectors installed near the pool heater. The carbon
monoxide detectors must be periodically inspected for proper operation so as to insure continued safety. Broken or
malfunctioning carbon monoxide detectors must be replaced immediately. If not fitted on the heater, the installer must
installed any safety devices according to the European Standard Codes of Practice.
NOTICE: UPON INSTALLATION THE INSTALLER MUST INSTRUCT THE USER IN THE OPERATION AND SAFETY
DEVICES AND PROVIDE A COPY OF THE HEATER’S USER’S
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