P/N 475114 Rev. F 8/2020 MASTERTEMP 125 Pool and Spa Heater Installation and User’s Guide
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PLUMBING CONNECTIONS
The MasterTemp
125 heater has the capability of direct PVC
pipe plumbing connections. A set of bulkhead ttings is
included with the MasterTemp 125 heater to insure conformity
with Pentair’s recommended PVC plumbing procedure. Other
plumbing connections can be used. See Figure 3 for plumbing
connections.
CAUTION
Before operating the heater on a new installation, turn on
the circulation pump and bleed all the air from the filter
using the air relief valve on top of the filter. Water should
flow freely through the heater. Do not operate the heater
unless water in the pool/spa is at the proper level. If a
manual by-pass is installed, temporarily close it to insure
that all air is purged from the heater.
WATER CONNECTIONS
The heater requires proper water ow and pressure for its
operation. See Figure 4 for the recommended installation. The
lter pump discharges to the lter, the lter discharges to the
heater, and the heater discharges directly to the pool or spa.
A manual bypass valve should be installed across the heater
when the pump flow exceeds 454 L/m (120 GPM). See
“WATER FLOW RATE” on page 5 - Table 1 for setting of
the manual by-pass valve.
Make sure that the outlet plumbing from the heater contains no
shut-off valves or other ow restrictions that could prevent ow
through the heater (except if the heater is below the level of the
pool/spa; as noted below, or winterizing valves where needed).
To switch ow between the pool and spa, use a diverter valve.
Do not use any valve that can shut off the ow. Do not use a
shut-off valve to isolate the heater unless it is below the level of the pool or spa.
Install the chemical feeder downstream of the heater. Install a chemical resistant one-way check valve between the heater
and the chemical feeder to prevent back-siphoning through the heater when the pump is off.
NOTICE: If the heater is plumbed in backwards, it will cycle continuously. Make sure piping from lter is not
reversed when installing heater.
Connect the heater directly to 50 mm (1.5 in - UK) PVC pipe, using the integral unions provided. Heat sinks are not
required. The low thermal mass of the heater will prevent overheating of the piping connected to the pump even if the
heater shuts down unexpectedly. Occasionally a two-speed pump will not develop enough pressure on the low speed to
operate the heater. In this case, run the pump at high speed only to operate the heater. If this does not solve the problem,
do not try to run the heater. Instead, correct the installation.
Do not operate the heater while an automatic pool cleaner is also operating. If the circulation pump suction is plugged
(for example by leaves), there may not be adequate ow to the heater. Do not rely on the pressure switch in this case.
If European Standard Codes of Practice require the installation of a pressure relief valve (PRV), see page 39 for
“PRESSURE RELIEF VALVE”.
Pool
Main
Drain
Spa
From Pool
3-Way
Valve
3-Way
Valve
3-Way
Valve
Chlorinator
Heater
Pump
Check Valve
Filter
Figure 4.
PUMP
FILTER
HEATER
MANUAL
BY-PASS
TO
POOL
GATE
VALVE
FROM
POOL
FROM
FILTER
Figure 3.
Section 1. Installation
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