Pentair Max-E-Therm

The Max-E-Therm is Pentair's other gas pool heater, sold under the Sta-Rite name, and its model numbers start with SR. It comes in 200, 333 and 400, each in natural gas, propane or heavy-duty, plus a 250 built to the ASME boiler code.

Mostly a MasterTemp, in its own cabinet

I set the parts tables from the two current manuals side by side. Of the 112 part numbers I counted in the Max-E-Therm's tables, 76 also appear in the MasterTemp's. They share the gas valve, igniter, switches, thermistor, control board, ignition module, and the heat exchangers and manifolds for the 200 and 400.

What's different is mostly the cabinet: a matte black resin enclosure Pentair calls Dura-Glas, with its own upper and lower enclosure kits. The other difference is the 333, a size the MasterTemp doesn't come in. Even that shares its heat exchanger, manifold kit and flameholder with the MasterTemp 300. Its blower and its gas and air orifices are its own.

So a dealer who stocks MasterTemp parts can fix most of a Max-E-Therm. It also explains why other heaters are sold as swaps for it. Pentair says the ETi 250 plumbs in where a MasterTemp or Max-E-Therm was, and Jandy says the same of its JXi.

Which one you have

The model number tells you three things. The number is the input, in thousands of BTU an hour. NA is natural gas and LP is propane. HD is heavy-duty, with a cupro-nickel heat exchanger that Pentair's catalog recommends for low pH, high flow or heavy use. It's rated 82% efficient against 84% for the standard copper one.

The 250 ASME (460767, or 460768 on propane) is a different build. It has an ASME-stamped heat exchanger with brass headers rated for a working pressure of 100 psi, schedule 80 CPVC connections and a 50 psi relief valve. Pentair's product page and manual list it. The 2025-2026 catalog doesn't, and the manual's flow table leaves it out, so its minimum flow isn't published anywhere I found. The 400 ASME is discontinued.

One more thing that doesn't add up: the brochure says the range runs from 175,000 BTU to 400,000. No Max-E-Therm 175 is listed on Pentair's product page, in the manual or in the catalog.

The keypad changed in May 2021

Pentair's catalog splits the keypad by date. Heaters made before 5/5/2021 take the five-button keypad, 472610Z. Heaters made after 5/6/2021 take the six-button one, 461106. The manual calls that one the RS-485 membrane pad and lists it beside the RS-485 control board kit, 461105.

RS-485 is what lets an IntelliCenter run the heater. Up to 16 heaters can share one IntelliCenter, each with its own address from 1 to 16, set from the heater's menu. The default is 1. While the IntelliCenter is in control, the heater's buttons do nothing and its display says "RS485 Control."

Older heaters, and other controllers, use the fireman's switch instead: remove the factory jumper and wire the controller or time clock across those two terminals. The circuit is 24 VAC at 0.5 A. Never put line voltage on it, and never touch a 24 VAC wire to a line-voltage terminal, which destroys the control board at once. For a heater without RS-485, the conversion kit 476211 brings the RS-485 control board, keypad and ignition module.

Flow, and the pressure switch

The minimum flow is 20 GPM for the 200, 33 for the 333 and 40 for the 400, and the maximum is 120 for all three. Above 120 you need a manual bypass, set once with its handle removed. The water goes pump, filter, heater, then straight to the pool, with no shut-off valve after the heater. Use a diverter valve to switch to the spa. A heater plumbed in backward cycles on and off continuously.

The troubleshooting chart has a second flow table, and it's wrong for this heater. It lists the MasterTemp's sizes, 175 to 400, and in one of its two copies prints the 400 as 0 GPM. Use the installation table.

A water pressure switch proves flow before the burner fires. It's set at 3.00 psi for a heater at pool level. The manual gives two rules for when to adjust it. One passage says below the pool or more than 2 feet above it. The warning box says more than 1 foot above or below. Beyond 5 feet above the water or 4 feet below, a pressure switch can't cope, and Pentair calls for a flow switch on the outlet pipe.

The manual adds two warnings. A two-speed pump on low may not make enough pressure, so run it on high to heat. And don't run the heater while an automatic pool cleaner is running.

The 68°F rule

This is the warning most likely to cost an owner a heat exchanger.

Pentair's manual says running the heater continuously on water below 68°F causes condensation that damages it and voids the warranty. Don't use it to protect a pool from freezing if you mean to hold the water below 68°F.

The manual isn't consistent about the thermostat, though. The control panel section says it goes as low as 65°F. The winter section calls 68°F "the heater's minimum setting." Whichever your panel allows, 68°F is the floor for any temperature you hold for long.

For a pool you use now and then in spring and fall, Pentair suggests setting it to 68°F and leaving it on, so the heater can bring the water back up in about a day. For a cold start below 50°F, run it continuously until the water passes 68°F. If the air is going to freeze, shut it down and drain it.

Checking the installation

A licensed professional has to install it, and the warranty depends on that. These are the numbers to check afterward.

• Gas: 4 to 14 inches of water column at the inlet, at least 4 while the heater runs, and no more than 2 inches of drop between off and running. The manual shutoff, sediment trap and union go outside the cabinet. A union inside it voids the warranty.
• The gas valve has a negative-pressure regulator set at −0.2 inches of water column. Pentair says never to adjust it, and to replace the valve only with an identical one.
• Voltage: it ships wired for 240 V with the red plug. For 120 V, the black plug from the control box goes in before the power is connected. If the 120 V plug is fitted and the heater is wired to 240 V, the transformer, control board and ignition module are destroyed. The reverse just won't run. Pentair doesn't recommend 208 V.
• Circuit: 14 AWG on 15 A. It draws about 5 A at 120 V and 2.5 A at 240 V, but needs the 15 A for the surge at start-up. Bond it to the pool equipment with solid copper no smaller than 8 AWG.
• Pump: it should run the whole time the heater does and for at least 5 minutes after. A time clock should turn the heater off through a fireman's switch at least 15 minutes before it stops the pump.
• Outdoors: never under a deck. Under a roof overhang, leave at least 3 feet above the vent and keep three sides open. Keep it 36 inches from an air conditioner or heat pump. Don't run it outdoors below −20°F. The bolt-down kit, 42001-0085S, is required in Florida and recommended everywhere.
• Indoors: it vents vertically as a Category I appliance, or vertically or horizontally as Category III, with 6 inches of clearance at the top, sides and vent.

The control panel on top turns to any of six positions, so it can face the way you'll stand to use it.

The smart bypass, and what the 35% means

Pentair's automatic bypass kit, 462048, puts a three-way valve with an IntelliValve actuator on the heater inlet and a check valve on the outlet. With BP-VALVE turned on in the menu, the valve takes 30 seconds to close when the heater calls for heat. After the heater stops, water keeps flowing through it for a one-minute cool-down, and then the valve sends the water around it again.

Pentair says the bypass saves up to 35% a year in operating costs. The footnote matters. The test used a MasterTemp 400 with an IntelliFlo VSF pump at 50 GPM, running the pump 3,000 hours a year and the heater 100, with electricity at $0.21 a kilowatt-hour. The saving is pump electricity: water that skips the heater meets less resistance, so the pump can run slower. Nothing in the test measures gas. The saving comes from the hours the heater isn't firing, 2,900 of the test's 3,000, so it's worth the most where the pump runs many more hours than the heater.

What the codes mean

• ERR PS — not enough water flow. It clears when flow returns. Clean the filter and skimmers first.
• ERR HLS — water leaving the first pass through the heat exchanger went above 135°F. It clears when the water cools below 135°F.
• ERR AFS — the blower isn't moving enough air. The heater waits 60 seconds, then has to be turned off with HEATER OFF.
• ERR IGN — the ignition module couldn't light the burner. Press HEATER OFF to clear it.
• ERR AGS — water after the second pass went above 140°F. The buttons stop working until you cycle the power.
• ERR SFS — the flue went above 480°F. Cycle the power to reset.
• E05 / E06 — the stack flue sensor reads open or shorted.
• E01 / 126 — the water temperature sensor reads open or shorted.

The menu's HISTORY item keeps the last five errors, and the menu also shows cycles, hours of heating, flue temperature and flame strength. Pentair's warning is plain: don't run the heater with any of these showing, and never jumper a safety switch to get past one.

Parts that split by build date

The tub was redesigned twice, and the parts follow the date, not the model.

• Heat exchangers split at 1/12/09. A 400 built after that date takes 474061, at $2,426.58 US list; before it, 77707-0234. The 200, 333 and the heavy-duty versions split on the same date.
• The combustion chamber and its cover split three ways: before 1/12/2009, the clamp-lid tub, and the 9-bolt lid. The manual dates the 9-bolt lid from 10/31/2013. Pentair's catalog and parts sheet say 11/16/2013.
• The 9-bolt lid's o-ring kit is 474952 in the manual and the catalog, and 474432 on the 2016 parts sheet. Order 474952, which is the one the catalog prices.
• The ASME heat exchangers split three ways as well, and again the manual and the catalog give dates a few weeks apart.

The rating plate inside the heater has the serial number. Read it before ordering anything in the heat exchanger or the combustion chamber.

The relief valve has two numbers in the same manual. It isn't fitted at the factory and some local codes require one. The maintenance section says to buy 460925, and the parts table lists 473715Z, which is also the one the catalog prices. Either way it must be a 3/4 in. valve set no higher than 50 psi. Pentair says any heater with a check valve or other restriction after it needs one.

Water chemistry

Put a chlorinator after the heater and lower than its outlet, with a check valve between them, R172288. Never put chlorine tablets in the skimmer. When the pump stops, that concentrated chlorine reaches the heater and corrodes the heat exchanger.

Pentair's chemistry table wants pH at 7.4 to 7.6, free chlorine at 2 to 4 ppm, salt up to 5,000 ppm with 3,200 ideal, and calcium hardness at 200 to 400. Total alkalinity is where the manual disagrees with itself: the table's ideal is 80 to 100 ppm, and the paragraph above it says 100 to 140. This site's alkalinity guide goes through why the right figure depends on whether your pH tends to climb or fall. Pentair doesn't cover heat exchanger damage from water chemistry.

Winterizing

Where it freezes, drain it. Turn off the power and the gas, and open the drain cock at the bottom of the manifold adapter. If the heater sits below the pool, close the isolation valves first. Blow the heat exchanger out through the pressure switch fitting with low-pressure air, under 5 psi, because higher pressure can burst parts. Then remove the pressure switch and plug its port, drain the manifold through the outlet pipe, and bag the air inlet grate against leaves and insects. Freeze damage isn't covered. Closing a pool for winter covers the rest of the pad.