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Pentair

Pentair MasterTemp Heater

MasterTemp accepts either a fireman's switch across two terminals or RS-485 on its COM port. Both are straightforward. What is not forgiving is the 24 VAC circuit behind the fireman's switch, which destroys the control board if line voltage reaches it.

Choosing between the two methods

Fireman's switchRS-485
WiringTwo conductors, dry contactTwo data conductors plus a common
Module outputH1 or H2 dry contactPORT A or PORT B
What you getOn or off onlySetpoints, status and alarms
Front panelStays usableButtons inactive, shows RS-485 Control

The fireman's switch is the simpler retrofit and works on any MasterTemp. RS-485 is the better result where the heater supports it, because faults surface in the app instead of on a panel nobody looks at.

Fireman's switch

The heater ships with a jumper fitted across the fireman's switch terminals, which is what allows it to run standalone. Remove that jumper and put your contact in its place. Closing the contact completes the heater's own 24 VAC control circuit and allows it to fire.

The factory jumper removed from the heater's fireman's switch terminals and replaced by a dry contact from the iSmart Module's H1 output, wired COM to N.O.
Replace the jumper, do not bypass it. Wire COM and N.O so the contact rests open.
  • The contact must be rated for 24 VAC at 0.5 A, because it carries the heater's own control circuit rather than a signal.
  • Use 18 AWG wire with at least 3/64 in (1.2 mm) insulation rated to 105 C.
  • Never apply line voltage to these terminals.
  • The fireman's switch circuit is protected by a 1.25 A fuse on the heater. A blown one points at a wiring fault, not a failed heater.
  • Route the wires through the knock-outs provided in the bottom of the control box.

RS-485

The heater's COM port is J4 on the control panel board, reached by routing the cable in through the exhaust panel. Pentair's own procedure calls for a drilled hole with a strain relief or flexible conduit and an insulating bushing, cable ties securing the run to the existing harness, and the wires kept off the exhaust.

PinColourSignaliSmart Module
1BlackCommonPORT terminal G
2GreenDATA-PORT terminal B
3YellowDATA+PORT terminal A
J4 pin order, with pin 1 on the left of the terminal connector.

Each heater on a bus needs its own address, set from the heater's front LCD menus. The default is 1 and the range is 1 to 16. A single heater can be left at the default.

When it does not fire

SymptomWhere to look first
Nothing on a heat callFactory jumper still fitted, or the contact wired across N.C instead of N.O.
Heater runs constantlyJumper left in place alongside the new contact.
Dead after wiringThe 1.25 A fireman's switch fuse, and then whether line voltage reached the control board.
Fires but cuts out earlyFlow or the heater's own limits. The contact only requests heat.
RS-485 wired but silentGreen and yellow swapped, or the heater address clashing with another device.

Sources