Pentair ETi 250 High-Efficiency Heater

The ETi 250 is Pentair's compact condensing gas heater: 250,000 BTU in, a titanium heat exchanger, and a two-line LCD control panel with a full menu. Pentair lists one version, 461112, factory set for natural gas. At 25 by 25 by 32 inches and 270 pounds, it's much smaller than the ETi 400, which is 30 by 34 by 42 inches and 379 pounds.

Pentair's catalog says its plumbing aligns exactly with the MasterTemp and Max-E-Therm, making it a drop-in replacement on tight equipment pads.

It's a professional install. Pentair's manual says a technician qualified in pool heater installation must install and service it, and that improper installation voids the warranty. What follows is what an owner should know.

Efficiency depends on the fuel

Pentair's headline is up to 96% thermal efficiency, and the footnote explains the "up to": the ETi 250 is 94% efficient on natural gas and 96% on propane with the conversion kit.

Altitude limits

The manual's first page sets hard limits, and says its 2,000 foot limit for propane, from the latest testing, supersedes anything in Pentair's other documents:

• Natural gas, up to 2,000 feet: as shipped.
• Natural gas, 2,000 to 10,000 feet: the high altitude conversion kit, 462057, must be installed. Pentair says gas flow has to be reduced at altitude for proper combustion and to avoid ignition problems.
• Propane: conversion kit 476370, and never above 2,000 feet.
• Above 10,000 feet: don't install it at all.

Pentair's warning is that getting this wrong can cause carbon monoxide poisoning or death.

What condensing means for an owner

The ETi 250 is a condensing appliance: its flue gases produce water while it runs.

• The water is acidic, pH 3.1 to 4.2. Pentair recommends its neutralizer kit, 476375, and says damage from untreated condensate isn't its responsibility.
• The drain needs a trap so flue gas can't escape through it. With no neutralizer fitted, Pentair says the condensate tubing must run through the heater's P-trap bracket.
• The heater has to sit level for that trap to work.
• Outdoors, it's for non-freezing weather. Pentair says not to operate it outdoors below 32°F, since the condensate line and trap can freeze and shut it down.

The flow window, and the automatic bypass

Pentair's manual rates the ETi 250 at 30 to 120 GPM, with a temperature rise across the heater of 25 to 35°F. For two or more heaters plumbed in parallel, it recommends 60 to 80 GPM each.

• Above 120 GPM, install a manual bypass valve before the heater, set it, then remove the handle or lock it.
• Paired with an IntelliFlo VSF pump, Pentair offers an automatic bypass using an IntelliValve actuator, kit 462048, which it says can add heater life and cut running costs. With BP-VALVE enabled in the menu, the valve takes 30 seconds to close on a call for heat, then after heating keeps water flowing through the exchanger for a one-minute cool-down before bypassing it again.
• A two-speed pump on low sometimes can't make enough pressure. Run it on high, and if that doesn't work, don't run the heater; correct the installation.
• Don't run it while an automatic cleaner runs. Pentair says a plugged suction line can starve the heater, and not to rely on the pressure switch to catch it.
• Water goes pump, filter, heater, pool. Plumbed backward, Pentair says, it cycles continuously.

After start-up, the outlet pipe should feel only slightly warmer than the inlet. If it's hot, or you hear boiling, flow is too low: check the filter, and if the temperature stays high, turn the heater off and call a technician. Pool heater not heating covers flow problems across makes.

The control panel and its menu

The display shows the water temperature on the first line and the setpoint on the second. POOL/SPA switches between the two, HEATER OFF turns the heater off, the arrows change the setpoint, and MENU/BACK and SELECT move through the menu. The HEATING light is solid while the burner fires and blinks during ignition.

The thermostat sets from 65°F to 104°F, and the setpoint has to be above the water temperature for the burner to fire. Pentair's factory settings are 70°F for pool and 95°F for spa.

The menu includes:

• POOL MAX and SPA MAX: the highest temperature each can be set to.
• HISTORY: the last five errors.
• CYCLES and RUNTIME: heater starts, and hours spent heating.
• RNC ALERT, RNC TIME and RNC RESET: the 1,000-hour neutralizer cartridge timer. Turn the alert off if you don't use a neutralizer.
• SFS TEMP: the current stack flue temperature.
• FLAME: the flame sensor's status, Normal or Low.
• HTR ADDR: the heater's address, 1 to 16, for automation.
• BP-VALVE: the automatic bypass, on or off.

Automation and timers

The ETi 250 connects to Pentair IntelliCenter over RS-485, up to 16 heaters, each with its own address set from the heater's menu. While IntelliCenter is in control, the heater's buttons are inactive, the display reads "RS485 Control", and alarms show on IntelliCenter's screens.

It can also be controlled through the fireman's switch terminals with a 2-wire control or a timer. Pentair says a pump timer should cut the call for heat 15 to 20 minutes before the pump shuts off, and that the connection must be a dry contact: powering it externally can damage the heater and isn't covered by the warranty.

What the error codes mean

• ERR PS: the water pressure switch is open, which means not enough flow.
• ERR AFS: the air flow switch, which checks the combustion blower.
• ERR HLS: the high limit switch opened, above 135°F at the exchanger outlet.
• ERR AGS: the automatic gas shut-off switch opened, above 150°F. Cycle the power to reset.
• ERR SFS: flue gas above 170°F. Cycle the power to reset.
• E06: a shorted stack flue sensor. E05: an open one.
• E01: an open water temperature sensor. 126: a shorted sensor, or water above 125°F.
• ERR CFS: the condensate float switch opened, usually a blocked drain or neutralizer.
• ERR IGN: the flame sensor. Cycle the power to reset.
• ERR FT: a thermal fuse opened.
• RNC flashing: the neutralizer timer has passed 1,000 hours of heating. Reset it from RNC RESET, or turn the heater off and hold HEATER OFF for 5 seconds.

Pentair's manual says only qualified technicians should troubleshoot the heater.

Where it can go

The placement rules match the ETi 400's:

• At least 5 feet from the inside of the pool or spa, unless a solid fence, wall or other permanent barrier separates them.
• Outdoors, in an open area on a level surface, away from debris, sprinklers, roof runoff and prevailing wind.
• Under an overhang, at least 3 feet between it and the top of the vent, open on three sides, and never under a deck.
• At least 36 inches from an air conditioner, heat pump or another gas heater, and 30 inches clear in front for service.
• In a garage or utility room, with its base at least 18 inches off the floor.
• A propane heater never in a pit or low spot where gas could collect.

Maintenance

Every six months, and at the start of each season: check the panels and vent for blockages, keep the area clear of anything combustible or corrosive, test the 50 psi relief valve by lifting its lever, and test the water pressure switch.

Every 12 months: Pentair says to have a qualified technician inspect and clean the heat exchanger, check its thermal insulation, and inspect the spark electrode and flame sensor. Pentair's cleaning kit, 461109, runs a water-fed brush through the exchanger on a cordless drill, with the burner removed and the exchanger left in place.

The neutralizer: check the pH at the cartridge outlet once a year, and replace the media when it falls below your local water authority's minimum.

Water chemistry, and the warranty

Pentair's manual lists these ranges for the heater:

• Free chlorine: 1 to 4 ppm, ideally 2 to 3
• pH: 7.2 to 7.8, ideally 7.4 to 7.6
• Total alkalinity: 60 to 180 ppm, ideally 80 to 100
• Calcium hardness: 150 ppm minimum, ideally 200 to 250
• Salt: 2,000 to 5,000 ppm, ideally 3,200
• Cyanuric acid: less than 30 ppm, following local codes
• Bromine: 2 to 10 ppm, ideally 4 to 6

The manual says failing to keep to these ranges can cause early heat exchanger failure and will void the warranty. It also says never put chlorine tablets in the skimmer, which floods the heater with concentrated chlorine when the pump stops, and to put any chlorinator downstream with a check valve, R172288, between it and the heater.

Winter

Where it freezes, Pentair's steps are:

1. Turn off power to the heater and pump at the breakers.
2. Close the gas valves, inside and outside the heater.
3. Open the drain at the bottom of the manifold and drain the exchanger and internal plumbing.
4. If the heater sits below the pool's water level, close the isolation valves.
5. Remove the water pressure switch and plug its port.
6. Drain the manifold through the outlet pipe.
7. Blow out the remaining water with a low-pressure blower, below 5 psi. Never use compressed air.
8. Cover the air inlet grate with a plastic bag.

Freeze damage isn't covered. In spring, don't turn the heater on until water is circulating. Closing a pool for winter covers the rest of the system.

Parts and prices

Pentair's 2025-2026 catalog lists the heat exchanger at $7,234.13, a little more than the ETi 400's. The gas valve is $709.22, the ignition control module $399.97, the control board $251.80, and the neutralizer kit $262.58. The high altitude and propane kits are $72.93 each.

Buying one

Pentair lists no online EC- version. When checked, the only Amazon listing that looked like it, titled "Pentair 250k BTU Pool Heater" at $7,999, gave no model number, so this page has no store link.

Where Pentair's documents disagree

• The gas valve setting. The manual's gas section gives the ETi 250's valve a manifold pressure of 1.4 inches of water column; its burner troubleshooting table says to verify –0.2 inches, the ETi 400's figure.
• The hold-down kit. The parts list gives 462055; the installation section says to buy 476004, the ETi 400's kit.
• Buttons that aren't there. The operating instructions say to press POOL ON or SPA ON and warn about a SERVICE HEATER light. The ETi 250 has a POOL/SPA toggle and shows errors on its LCD.
• The neutralizer reminder. One page says the display shows REPLACE after 1,000 hours; another says RNC flashes.
• The thermal fuse code. ERR FT in the fault table; ERR TF in the safety controls text.
• When a flow switch is needed. One page says more than 1 foot above or below the deck; another allows resetting the pressure switch up to 3 feet.
• The lowest thermostat setting. 65°F in the control section, 68°F in the winter section.
• Chlorine and alkalinity. The text gives chlorine floors of 0.6 and 1.4 ppm and alkalinity of 100 to 140 ppm; the table gives 1.0 ppm and 80 to 100 ppm ideal.
• Salt. The table lists it twice, once as 3,000 to 4,500 ppm with 3,250 ideal, and once as 2,000 to 5,000 with 3,200 ideal.
• The membrane pad. 476201 in the 2022 manual, 461106 in the 2025-2026 catalog.