Why did my pool pipes freeze over the winter?

Water was still in the plumbing

Pool pipes freeze for one reason: they held water when the temperature dropped below freezing and nothing kept it moving or warm. The pump housing, filter tank, valve, heater and the above-ground runs between them hold the most. The damage often shows at the equipment pad and short exposed pipes.

The physics is simple. When water freezes in a pipe, it expands the same way.^[4] But it is not the ice pushing outward that breaks the pipe. After a complete blockage forms, further freezing raises the water pressure between the ice and a closed point, and it's this increase in water pressure that leads to pipe failure.^[4] Usually the pipe bursts where little or no ice has formed.^[4] That is why a split can appear in a fitting a few feet from the frozen section.

The usual ways it happens

• The system was never drained. Hayward's pump manual says to drain all water from pump and piping when expecting freezing temperatures or when storing the pump for a long time.^[1] Hayward's filter manual says to completely drain the tank by unscrewing the drain cap at the base of the filter tank, and to leave the cap off during winter.^[2] A cap screwed back on, or a pump drained once and refilled by rain, holds water that can freeze.
• Lines were closed with water in them. Skimmer and return lines that were plugged without being cleared are common freeze points.
• The pool was left running or half-closed. A pump turned off during a cold night with water still in the heater and filter has nothing to protect it.
• The wrong antifreeze. Use only propylene glycol as antifreeze in a pool or spa system, because other types are highly toxic and may damage plastic components.^[1]
• Relying on the heater. Raypak's manual says: do not use the heater to maintain water temperatures just above freezing or for freeze protection.^[3] The heater is not warranted against freeze-ups.^[3]

What you can do now

Start with the power off. A cracked pump or filter should not be run, so keep the breaker off until the parts are inspected. Then walk the equipment pad and look for hairline cracks in the strainer housing, a split filter tank, cracked unions and valves, and wet gravel or a drip under any fitting.

You can safely drain what still holds water, using the drain plugs and drain cap the manufacturer provides. Photograph every crack with the equipment labels in view, because that record matters for a warranty request or an insurance claim. Do not expect the maker to pay: Allowing the pump to freeze will void the warranty.^[1] The limited warranty excludes damage from freezing, negligence, improper installation, improper use or care or any Acts of God.^[2]

Wait for a full thaw before judging the damage. A cracked fitting can hold while frozen and leak once the ice melts, and a pool company can pressure-test the lines to find the rest.

Do not use compressed air to clear lines

Many owners reach for a shop compressor. Hayward's warning is blunt: purging the system with compressed air can cause components to explode, with risk of severe injury or death.^[1] The manual allows only a low-pressure (below 5 PSI), high-volume blower for air purging the pump, filter or piping.^[1]

Plugs used in winter closing also have to come out before the pool reopens. Failure to remove pressure test plugs and/or plugs used in winterization of the pool/spa from the suction outlets can result in an increase potential for suction entrapment.^[2]

Stop and call a pro if

• The heater is wet or cracked. Do not open it or touch gas or wiring yourself. A frozen gas heater needs a licensed technician.
• Water leaks from buried or in-wall pipe. Soggy ground, a falling water level that does not match the evaporation, or air in the pump basket point to a split line you cannot see.
• The pump motor or wiring got wet. Leave it unplugged and unpowered until a technician has dried and tested it.
• Pressure rises or the filter leaks after thawing. Replace the part, do not tape it.
• You do not know what was plugged. A technician can find every winterization plug before anyone starts the pump.

Prevent it next winter

Close the equipment properly before the first hard freeze. How to winterize an above-ground pool covers the job, should I winterize my pool myself or hire a pool company helps you choose, and how much pool winterizing costs in Virginia lists what to ask for in a written quote.

Loclis lists Virginia pool and equipment businesses: browse pool equipment repair or read more pool equipment answers.

When you are ready, describe the damage once and local pool companies quote it.