What Happens If I Don’t Close My Pool?

If you have closed your pool already, then I say congratulations and sorry at the same time – congrats for getting it done already and sorry your summer is over. This blog post however, is not about crying for the season passed, but for folks out there with a pool, thinking they might leave their pool open for the winter.

You may want to close your pool before the weatherman gives frost warnings in your area – we’re about to show you what happens if you don’t close your pool and have even just occasional winter temperatures below the freezing mark.

Fair warning, it’s not pretty. Some of the images might make you break out in a cold sweat and give your wallet and bank account a case of the shivers. So . . .

Q: What happens if I don’t close my pool?
A: It falls apart.

There you have it in plain terms. Don’t believe me? I’m not trying to scare you, but there are a whole host of potential damage that could occur to pools – if the pumps aren’t running when temperatures dip below freezing. Let’s move on to specifics.


One of the most important things you do when closing a pool is ensuring the pool water level is below the your pool filter system intake along with getting all the water out of your pool equipment and pipes.

If there is any water left in the pipes of your pool plumbing, the water will freeze, and Physics 101 class tells us water expands when it freezes, up to 10%, and that’s enough to crack pipes, pumps, filters, heaters, skimmers, and other things – that are full of water.

If pool pipes or equipment is only half full of water for example, there may be enough space for the ice to expand into, maybe. But until you’ve done some winterization, your pool equipment and pipes are likely very full of water.

If you have an above ground pool with the pool filter system and plumbing above ground (like nearly all above ground pools), pipes and pumps can freeze up in less than an hour of minus 32 degrees. The same is true for inground pool equipment that is not running when temperatures are below freezing. As long as water is moving through all pipes and all equipment, nothing will freeze.

Water in underground pipes won’t freeze right away, it takes several days of below freezing temps before the soil freezes. I’ve been told that the frost goes into the ground about an inch per day, when temps remain below 32°, day and night, for long periods of time. Daytime warm-ups can thaw soils just as rapidly, however. As such, it can take a week or two of consecutive days below freezing, before (well-buried) pipes are in danger of freezing.


a pool pump leaks in many places after water inside it freezesThis is what a pool pump looks like when you turn it on after it was damaged by ice. At least PVC pipes and connectors are rather inexpensive and easy to replace. Depending on what type of pool pump you have, buying a new pump housing can cost several hundred dollars more than PVC pipe.

To winterize a pool pump (even if just for one night), remove the 2 plugs from the pump.


And don’t think your pool heater is stronger. Cast Iron and Polymer heater headers are usually the first thing to snap in a sudden freeze. And it’s fortunate that they do, which drains the heater and avoids much great damage.

To winterize a pool heater (even for just one night), remove the front and rear header drain plugs, and disconnect the pressure switch inside the heater. Blowing air through the heater is recommended, to remove all of the water.


Your pool filter tank can withstand enormous pressure, up to 50 psi in most cases, but that’s still no match for the power of expanding ice. In some cases, the tank itself will crack, or the clamp ring on cartridge or DE filters will crack in half, or the top mounted multiport valve flange will separate from the tank, or just start leaking, as shown here.

To winterize a pool filter (even just for one night), open the air bleeder and remove the filter drain cap or drain plug. If you have a multiport valve, turn the handle to a spot in between any two positions, and if you have a push-pull slide valve, place it mid-way between up and down positions.


For inground pools, that nasty spring opening surprise could be even worse because your pool pump and filter will start going, and then you’ll notice the equipment isn’t working right and wonder why. It’s because you can’t see the broken pipes that are leaking three feet under your concrete pool deck.

Replacing busted up pool plumbing is one thing, having to cut through your concrete pool deck and dig down several feet to fix the plumbing is quite another thing. Let’s not forget, if your pipes are freezing, there’s probably a real good chance your pool equipment is too.


If you have an above ground pool, there’s something unique that can happen if you don’t use an air pillow or don’t winterize the skimmer properly, they crumple like tin cans.

An above ground pool is designed to contain the water inside of it, but as an ice sheet thickens across the pool, it puts outward stress on the walls. When the ice sheet is also frozen inside the skimmer – any heaving, tilting or slipping of the ice sheet can wreak havoc on even the strongest aboveground pools. In this case, a water leak left no support for a 6″ thick ice sheet.

If you still want to keep the pool open, In The Swim carries the lifesaving Intermatic freeze sensor, compatible with with the PE153 Digital Timeclock. This allows you to pre-set a temperature for the pump to turn on, automatically (so you don’t have to).

Or, if you go ahead an winterize, don’t forget Air Pillows and Skimmer Plugs to protect your pool, and for inground pools, new winter pool plugs and pool cover supplies are in order. And every well-winterized pool can find a cheap insurance policy in pool anti-freeze.

If it’s too late to winterize, and if your pool equipment is already frozen, remove the drain plugs, throw heavy blankets or tarps over the equipment, and set-up a small space heater with plenty of ventilation, you don’t want it to catch on fire next!

For those of you on the fence, you should seriously consider going the pool closing route. Now is the time to do it, and if budget is an issue, In The Swim offers some nice winter covers along with pool winter kits at good prices, right now.


Larry Andersen
InTheSwim Staff Blogger



What Happens If I Don’t Close My Pool? — 11 Comments

  1. I didn’t get around to covering our above ground pool. It was closed cleaned and disconnected from the pump, just uncovered. I have made sure the kids would go out and do a bit of brushing and removing leaves and then we had to leave town unexpectedly. The pool looks frozen solid. It’s been this way for about 2 weeks an will probably be another week or 2 befor our temps go above 32. What’s the best thing for me to do at this point?

    • Hi, without an air pillow, aboveground pools can freeze solid, and this puts pressure on the pool walls, so is best avoided. You can bust thru the ice carefully if it is thin, and place several 6-12 gallon milk or water jugs with a few inches of pea gravel inside, to float in the pool, and absorb ice expansion, or keep the pool from freezing solid across. If you want to try to melt the ice, if it was only an inch or so thick, you could maybe use a heating cable…? If it is several inches thick, I’m not sure what you can do, maybe a floating pond heater, or just wait and hope for no damage…? If you try to bust up a thick ice sheet, it can easily shift, and cause the damage you are trying to avoid.

  2. We weren’t able to close/wonterize our inground pool. We had a family emergency that required us to tend to our baby. t’s been below freezing for a few days and the pool is frozen. It looks like the pump and stuff is also frozen. We have a pool heater. All have been turned off for a few weeks. We’re trying to get a company to come close it immediately (if possible). Should I take a heater out to try to thaw the equipment and turn it on along with the heater? Did we ruin our pool, pipes, equipment? 🙁

    • Hi Tara;

      If you find your pool equipment frozen, the first thing to do is cover with heavy woolen blankets, and place a small space heater, and remove the drain plugs on the pump(s), filter, heater, chlorinator, to drain all of the aboveground equipment. In your case, and in most cases like this, one or more parts of the equipment may have frozen and cracked. Usually the pool heater header will crack first, and this relieves the pressure, and allows some water to drain. In more severe cases, inline valves or the pump may crack. You should be able to see most cracking, if you inspect your aboveground equipment and pipes closely, but heater damage is sometimes harder to see. The pipes underground are likely OK, without damage. In most cases like this, you can expect repair costs in the $500-$1500 range. Not too bad, I hope. Good Luck!

  3. I plan to leave my pool open all winter in NENC. I will leave the pump running 24/7 just like I do in pool season. I hope for the best, we have never been 32 degrees below zero. I figure with the pump running, I should be ok…..

    • Hi Judy, I hope i didn’t say 32 degrees below zero! At 32°, or lower, pipes and pumps could freeze, if the water is not moving thru the pipes. In NE NC, you will get some below freezing temps, but as long as the pump is running, and all the pipes are open (no closed valves), the water won’t freeze, and you’ll have no problems. The pool surface may freeze, but that should not be a problem, again as long as the pump is running, it won’t freeze very thick-ly. The one big worry you may have is a power outage, or pump motor failure. In both cases, if temps are below 32°, remove the filter and pump drain plugs as fast as you can, and throw a heavy blanket(s) over the filter system, maybe place a small space heater if needed, if you have power.

  4. I always drain in ground pool pipes, shop vac or blow out the water and add at least 1.5 gallons of the pink RV antifreeze and plug up the the pool side inlets to prevent water from entering the return and skimmer pipes as the winter rain and snow melt refill your pool. for the bottom drains pour 2 gallon of the antifreeze into the pump side pipes until you see some pink come out of the bottom drains. The pink antifreeze is non toxic never use the green version in you pool or allow it to drain on the ground. (or use pool antifreeze – editor)

  5. Hi what are your thoughts about winterizing the plumbing but keeping the pool uncovered. I have an inground on long island NY. What are the risks assuming I rake and swirl in chemicals every so often?

    Thank you for your input

    • Hi Arthur, sure you can do that! The main risk is staining from excessive leaves and such just sitting on the pool floor. But, if you are able to clean the pool every few weeks, and you don’t mind using extra chemicals (fall and spring – cleaning or chemicals many not be needed Nov-Feb), you’ll be fine. Here’s a related blog post from another well respected blogger on another well respected pool blog. 🙂 Can I Keep my Pool Uncovered all Winter?

  6. Living in the northeast, how do I keep my winter cover on my above ground 16 x 36 pool from blowing up all over? 50% of my pool is surrounded by a deck. Doesn’t take long for it to become wind damaged.

    • Hi David, there are 3 products to prevent wind problems on aboveground pool covers. Cover Seal, like a giant roll of saran wrap, no go in your case. Cover Clips, used every 2 ft or so, to clip the cover to the pool top rail, and also Wall bags, placed on the inside edge of the cover, or run thru the cable, to provide more support. For the part that is surrounded by deck, I would also think cover clips. there is another one too, called cover cliploc jr., which we don’t carry. So, essentially, clip the cover to the pool, and or weigh down the cover edge, or put weights on the cable, and have a tight cable. Also, a little bit of water left on the surface, just 1/4″ to 1/2″ across the surface, can help hold down the cover.

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