It's easy to assume pool equipment in the East Valley never has to think about freezing. It does. Not often, and not for long, but most winters bring a few nights cold enough for the equipment to react, and that's when owners notice the pump running at 3 a.m. and wonder what's wrong. Usually nothing is. This guide covers how often it actually gets that cold here, what your pump and automation are designed to do about it, and what to check before a cold night.

How often the East Valley freezes

We counted freezing nights, a minimum of 32°F or lower, in NOAA's daily records (NOAA ACIS):

East Mesa (NOAA cooperative station 022782): at least one freezing night in 22 of the 23 winters with complete records from 2002-03 to 2025-26, and an average of about 10 a winter. About two nights a winter reached 28°F or colder. Over the last ten winters the average was about seven, from none in 2025-26 to 13 in 2018-19. The earliest freeze in the record was November 27 and the latest April 5. The coldest night was 20°F, in the winter of 2006-07.
Phoenix Sky Harbor: freezing nights in only 8 of the last 30 winters, and none since January 2, 2019.

The difference is the point. The airport, in the middle of the city, rarely freezes. East Mesa, on the eastern edge of the metro, does most years. These are single stations: a yard on open ground, in a low spot or at the edge of town can be colder, and a yard surrounded by buildings can be warmer. We didn't find a long NOAA temperature record for Queen Creek or San Tan Valley, so we haven't put a number on them.

What "freeze protection" actually means

On most pool systems, freeze protection means running the pump when it's cold to keep the water circulating. The question is what decides it's cold, and whether that decision covers the whole pool or just the pump.

Automation: the air sensor decides

If your pool has automation, it has an air temperature sensor, and that's what freeze protection relies on.

Hayward AquaLogic and ProLogic: with freeze protection enabled, when the air sensor falls below the freeze threshold the system turns on the filter pump to circulate the water (AquaLogic manual, p. 4). The threshold is adjustable from 33°F to 42°F, with 38°F as the default. On a pool and spa system the valves also alternate between pool and spa every 30 minutes, and the chlorinator won't run if freeze protection is the only reason the pump is on (AquaLogic manual, p. 20). While it's that cold, you can't manually turn off equipment that has freeze protection enabled (p. 4).
Pentair IntelliCenter: when freeze protection is active, the pump runs at the freeze speed that's been set for it. Pentair notes that on IntelliCenter, setting the freeze speed for pumps at addresses 2 to 16 means turning freeze protection off first, unlike EasyTouch and IntelliTouch (IntelliCenter guide, p. 2).
Jandy AquaLink RS: if the system is set up to use the air sensor as a solar sensor, the air temperature is no longer read, and Jandy says an adjustable freeze kit must be added for freeze protection (Jandy AquaLink RS manual, p. 20). If you have solar heating on a Jandy system, it's worth knowing which way yours is set up.

The pump's own cold-weather mode is not freeze protection

Most variable-speed pumps have their own cold-weather setting, and the manufacturers are clear that it protects the pump, not the pool.

Pentair IntelliFlo VS+SVRS, Thermal Mode: the sensor is inside the drive, on top of the motor. You can set the speed it runs at, from 1,100 to 3,450 RPM, and the temperature it starts at, from 40°F to 50°F, with 40°F the default. Pentair's note is direct: the feature is for protection of the pump, and you should not depend on Thermal Mode for freeze protection of the pool. The pump can sense a different temperature than the actual air, it doesn't sense water temperature at all, and the automation's air sensor should be used to sense the real temperature (IntelliFlo VS+SVRS manual, p. 18). When the pump is connected to an automation system, its own Thermal Mode is disabled and freeze protection comes from the automation (p. 27).
Pentair IntelliFlo3 VSF: Thermal Mode is intended to help protect the pump in freezing or near-freezing conditions, and Pentair says not to depend on it for the entire filtration system and pool (IntelliFlo3 VSF guide, p. 9). It's controlled by the drive's internal temperature, not the water's (p. 11).
Hayward TriStar VS, Low Temp Operation: when the pump is stopped and the temperature drops below the set point, it primes and runs at its maximum allowed speed for 8 hours. It isn't active when the pump is controlled remotely, and Hayward says it is not intended to protect the pump, plumbing or pool from freezing (Hayward TriStar VS manual, p. 18). On the TriStar VS 950, Hayward notes the setting reacts to the drive's internal temperature, which doesn't correlate with the outside air (TriStar VS 950 manual, p. 21). Hayward also says the drive itself is designed to withstand temperatures below freezing (Hayward TriStar VS manual, p. 6).
Pentair SuperFlo VS: Pentair says the owner is responsible for determining when freezing conditions may occur, and that in mild climates where temporary freezing can happen, you should run the filtering equipment all night (SuperFlo VS manual, p. 14).

So a pump on a plain timer, with no automation, is relying on its own pump-protection setting at best. On a night forecast to freeze, Pentair's advice for mild climates is the simple one: run it.

Why your pump is running in the middle of the night

If it's a cold night and the pump is running when it isn't scheduled to, that's very likely freeze protection or the pump's own cold mode doing what it's designed to (AquaLogic manual, p. 4). A TriStar in Low Temp Operation runs for 8 hours (Hayward TriStar VS manual, p. 18), and an IntelliFlo3 reports Thermal Mode as an alert when it's running for that reason (IntelliFlo3 VSF guide, p. 11).

The thing not to do is turn it off and leave it off on a freezing night.

Ways freeze protection gets switched off by accident

Service mode. On a ProLogic or AquaLogic, service mode cancels scheduled automation and suspends freeze protection (Hayward ProLogic guide, p. 37). The AquaLogic's timed service mode returns to normal on its own after 3 hours; plain service mode stays on until someone turns it off (AquaLogic manual, p. 5). Don't leave the panel in service on a cold night.
System Off. The red System Off button on an AquaLogic remote keypad turns every output off until it's pressed again, and Hayward warns it overrides freeze protection and may cause damage in freezing conditions (AquaLogic manual, p. 5).
A failed air sensor. If freeze protection is enabled and the air sensor reads open or short circuit, the AquaLogic lights Check System (AquaLogic manual, p. 38). With a bad sensor, the system can't tell it's cold. See Hayward ProLogic Check System messages.
A breaker that's off, or a pump that has stopped on an alarm. Freeze protection can only run a pump that has power and isn't faulted. See pool pump not working after a power outage.

What to check before a cold night

Look at the forecast low for your area, remembering that outlying yards can run colder.
If you have automation, check that freeze protection is enabled, the panel isn't in service mode, and there's no Check System or sensor message. If you're not sure how it's set up, that's a quick thing to look at on a diagnostic visit.
If your pump is on a plain timer, follow Pentair's advice for mild climates and let the filtering equipment run through the coldest part of the night (SuperFlo VS manual, p. 14).
Make sure the pump is moving water, not just humming: baskets clear, the pump primed, the valves open.
A heat pump may stop on its own. A Pentair UltraTemp can show LOW AMBIENT TEMP when the air is too cold for it, and LOW WATER TEMP when the water is below 40°F. See Pentair UltraTemp alarm messages.

Pentair's manual separates full winterizing, which means draining the pump, from what it suggests for mild climates (SuperFlo VS manual, p. 14). Hayward's instructions for that are to drain the pump and piping and to use only propylene glycol as antifreeze in a pool system (Hayward TriStar VS manual, p. 23). If you think you need to winterize, ask first.

If something did freeze

If you find water on the pad after a cold night, turn the equipment off and see pool equipment leak repair.

When to call

Call if freeze protection isn't running the pump on a cold night, if the panel shows an air sensor or Check System message, if a pump or heat pump keeps stopping on an alarm in cold weather, or if you find a leak after a freeze. We check the air sensor, the freeze settings and the pump, and tell you what has failed and what putting it right involves before anything is quoted.

If you don't know what's wrong, a diagnostic is $120, and it's credited toward your repair if you go ahead. Start from pool automation repair or variable-speed pump repair, or answer a few questions in the Pool Problem Finder. For IntelliFlo alarms, including Thermal Mode, see the Pentair IntelliFlo alarm guide.

Sources

Every statement above links to this list. Manual page numbers are the printed page numbers.

NOAA Regional Climate Centers, Applied Climate Information System, daily minimum temperatures for East Mesa (cooperative station 022782) and Phoenix Sky Harbor, winters 1996-97 to 2025-26, queried October 28, 2026. The same records are available through the National Weather Service Phoenix NOWData page. A winter runs July to June; a freezing night is a minimum of 32°F or lower; winters with fewer than 330 days of data are left out.
Pentair, IntelliFlo VS+SVRS and IntelliPro VS+SVRS Variable Speed Pump Installation and User's Guide, P/N 356916 Rev. D (11/6/23).
Pentair, IntelliFlo3 VSF and IntelliPro3 VSF Variable Speed and Flow Pump User's Guide, P/N 356088 Rev. C (5/30/23).
Pentair, SuperFlo VST, SuperFlo VS and SuperMax VS Variable Speed Pumps Installation and User's Guide, P/N 356292 Rev. A (7/10/20).
Pentair, IntelliCenter Pool Control System Troubleshooting Guide (02/2023).
Hayward, 2.70 THP VS Pump Family Owner's Manual (TriStar VS), 1011786 Rev B.
Hayward, TriStar VS 950 Owner's Manual, IS32950VSP Rev B.
Goldline Controls (Hayward), Aqua Logic Automation and Chlorination Operation Manual, 092043H (2008).
Hayward, ProLogic/AquaLogic Troubleshooting Guide, Residential, TSG-PL447c.
Zodiac (Jandy), AquaLink RS Troubleshooting Manual, 6919 Rev E.

Pentair, IntelliFlo, IntelliCenter, SuperFlo, EasyTouch and IntelliTouch are trademarks of Pentair. Hayward, TriStar, ProLogic, AquaLogic and Goldline are trademarks of Hayward Industries. Jandy and AquaLink are trademarks of Zodiac Pool Systems. They are named here only to identify equipment.

Pool freeze protection on cold East Valley nights