Pentair MT125 - Plumbing Connections

MASTERTEMP 125 Pool and Spa Heater Installation and User’s Guide 460906 Rev. D 8/2020
12
PLUMBING CONNECTIONS
The MasterTemp
®
125 heater has the capability of direct
schedule 40 PVC plumbing connections. A set of bulkhead
ttings is included with the 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 ow exceeds 70 GPM (265 LPM ). See
“WATERFLOWRATE”Table1onpage14 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 for pool installations 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.
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: MULTIPLE HEATER INSTALLATION: Seepage13,formultipleMasterTemp125heaterandFlowMeter
installations.
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 3.81 cm (1.5”) 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. If you are using a exible corrugated hose for above ground systems, use only Pentair approved
exible hose kits: P/N 155151 (1.8 cm - 6 ft.) and P/N 155005 (36.5 cm -12 ft.).
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.
Pool
Main
Drain
Spa
From Pool
3-Way
Valve
3-Way
Valve
3-Way
Valve
Chlorinator
Heater
Pump
Check Valve
Filter
Figure 4.
Section 1. Installation Instructions
PUMP
FILTER
HEATER
MANUAL
BY-PASS
TO
POOL
GATE
VALVE
FROM
POOL
FROM
FILTER
Figure 3.