How to put winter plugs in a swimming pool?

What are winterization plugs used for?

During passive winterization, the filtration system is turned off for the entire winter. Water remaining in the pipes could freeze, expand and crack a pipe, fitting or sealed component. To prevent this, the water level is lowered, the pipes are drained, and then the openings on the pool side are sealed.

The plug thus prevents pool water from returning to the circuit. It is generally made of rubber, conical in shape, with a wing screw: tightening the screw compresses the rubber and causes it to expand against the wall of the opening.

During active winterization, where the filtration system continues to operate, plugs are generally not used on the return jets, as water must circulate.

Where to place the plugs?

Draw a small diagram of your pool showing the location of each opening and the measured diameter. This plan will be useful every autumn and will prevent you from forgetting a return jet when closing the pool.

Identify all the openings in your pool before you start: return jets, vacuum port, skimmer outlets, and possibly the main drain, depending on your installer's recommendations. The number of plugs required depends on this.

For skimmers, a skimmer compensator is often used as well, a part that absorbs the pressure of the ice. The plug seals the pipe located at the bottom of the skimmer.

What size plug should you choose?

This is the most common question. The correct size depends on the internal diameter of the opening or pipe to be sealed. Measure it with a tape measure or, more precisely, with a caliper.

• Measure each opening: return jets, the vacuum port and skimmers do not always have the same diameter.
• Choose a plug whose tightening range covers your measurement.
• If in doubt between two sizes, ask for advice rather than forcing a plug that is too large.
• Keep a spare plug: it is common to misplace one from one year to the next.

In our shop, you will find, among others, a 50 mm conical rubber plug with a wing screw, and a 3-inch nylon plug for openings measuring 74 to 86 mm.

Step-by-step guide to installing the plugs

1. Finish preparing the water: cleaning, balancing the pH, and distributing the winterization product with the filtration system running.
2. Lower the water level below the return jets and skimmer mouth, following the manufacturer's recommendations, especially for a pool with a liner.
3. Stop and purge the filtration system: drain the pump, filter and pipes according to your installation's instructions.
4. Remove the decorative covers or adjustable return jets if necessary, to access the opening.
5. Insert the plug straight, with the conical part in the opening.
6. Tighten the wing screw by hand, gradually, until the plug holds firmly without forcing it.
7. Check that it no longer turns and does not come out when you pull it gently.

Plugs and other frost protection

Plugs are only one part of the system. Complete passive winterization generally combines several protections, each with its role:

• Plugs seal the pipes on the pool side, once they have been purged.
• The skimmer compensator is placed in the skimmer and absorbs the pressure of the ice, which could otherwise crack the skimmer body.
• Winterization floats, placed on the water surface, absorb part of the pressure of the ice against the walls. Their use depends on the type of pool and the manufacturer's recommendations.
• The winter cover limits the entry of leaves and light, and protects the treated water.
• Draining the equipment (pump, filter, and possibly heat pump) is done according to their instructions: open the drain plugs, and move sensitive parts to a dry place if possible.

None of these protections replaces the others. A perfectly installed plug does not protect a filter left full of water in an unheated room.

Checking the watertightness of a plug

After installation, take a few minutes to check each plug. Once the level has been lowered, a properly tightened plug should not allow water or air to pass through. If you notice a leak, loosen the screw, reposition the plug straight, and tighten it gradually.

Over time, the rubber can harden or crack, especially if it has been stored in the sun. A plug that no longer expands correctly must be replaced: it costs much less than a pipe cracked by frost.

Errors to avoid

• Sealing without purging: water remaining in the pipe can freeze despite the plug.
• Overtightening the wing screw: you risk damaging the sealed component or the plug.
• Choosing a plug that is too small, which barely holds and eventually falls out.
• Forgetting an opening, such as the vacuum port, which is often less visible than the return jets.
• Reusing an old cracked plug without checking that it still expands correctly.
• Allowing the water level to rise above the return jets due to rain, without monitoring.

During winter and in spring

After each frost or heavy rain, check the plugs and the water level. If the water has risen above the return jets, lower it again. A plug that has moved must be retightened.

In spring, when restarting the system:

1. Clean the cover and remove it.
2. Raise the water level to the normal operating height.
3. Loosen the wing screw and remove the plugs.
4. Reattach the return jets, decorative covers and equipment, then restart the filtration system.
5. Rinse and dry the plugs before storing them away from light for the following winter.

And for a pond or garden pool?

Winterization plugs are also used for certain garden pools equipped with PVC pipes, for example when a pump or filter is removed and stored indoors for the winter. In this case, sealing the openings helps maintain the water level of the pool. Our article on good practices for ponds in winter details the precautions specific to ponds with fish.

Frequently asked questions

Where to place the winterization plugs in a pool?

In the return jets, the vacuum port and skimmer pipes, after lowering the water level and purging the circuit.

What size winterization plug should you choose?

Measure the internal diameter of each opening and choose a plug whose tightening range covers this measurement.

Are plugs needed during active winterization?

Generally not on the return jets, as the filtration system continues to operate. Plugs are mainly used during passive winterization.

How to tighten a winterization plug?

Insert it straight, then tighten the wing screw by hand until the rubber expands and the plug holds firmly.

What should you do if the water level rises during winter?

Lower it again below the return jets and check that the plugs are still properly in place.

Can winterization plugs be reused from year to year?

Yes, if they are rinsed, dried and stored away from light. Replace a plug whose rubber has hardened, cracked or no longer expands correctly when tightened.

Read also

• How many main drain openings in a pool?
• How to set up your pool equipment room?
• How to clean an above-ground pool after winter?