Frozen Pipes in Ontario: Thawing Safely and Avoiding a Burst

With frozen pipes in Ontario, the safe approach is to open the affected tap, warm the pipe slowly with a hair dryer or heating pad starting at the tap end, and never use an open flame. Find your main water shutoff before you start, because a pipe that split while frozen will only begin leaking once the ice melts. Most freeze-ups can be thawed without damage if you go slowly and watch for leaks.

How to tell a pipe is frozen

• A tap gives a trickle or nothing at all during a cold snap, while other taps in the house work normally.
• Only the hot or only the cold side has stopped.
• You can see frost or a bulge on an exposed section of pipe.
• A toilet will not refill after flushing.
• The problem fixture is on an outside wall, over an unheated crawlspace or garage, or in a cold corner of the basement.

If no tap in the house has water, the line coming in from the street may be frozen, or there may be a problem with the municipal supply. Call your municipality's water department before you try anything yourself.

Why frozen pipes burst

Water expands as it freezes. The ice plug itself is usually not where the pipe fails. As ice grows along the pipe, it squeezes the water trapped between the plug and the closed tap, and the pressure there rises until the pipe or a fitting gives. That is why a split is often found in a section that was not frozen at all, and why the flood starts hours later when things warm up and the ice lets go.

How to thaw frozen pipes safely

1. Locate the main shutoff beside the water meter and make sure it turns. If you see a crack or split in the pipe, close the main before you thaw anything.
2. Open the tap the frozen pipe feeds, both hot and cold. Running water helps melt ice and gives pressure somewhere to go.
3. Find the cold section. Feel along exposed pipe for the coldest spot, and check where the line passes along outside walls and rim joists.
4. Apply gentle heat, starting near the tap and working back toward the frozen section. Use a hair dryer, an electric heating pad wrapped around the pipe, or towels soaked in hot water.
5. Warm the space as well. Open the cabinet doors under a sink on an outside wall, and set a portable heater in the room at a safe distance from anything that can burn. Do not leave it unattended.
6. Keep going until full flow returns, then check the whole length of the pipe and the ceiling or floor below it for drips.
7. If the frozen section is inside a wall or ceiling you cannot reach, turn up the heat in the house and call a plumber.

What not to do

• Do not use a propane torch, heat gun on high, kerosene heater or any open flame. This starts house fires and can boil water inside the pipe.
• Do not use electrical appliances while standing in water.
• Do not hammer or bend the pipe to break up ice.
• Do not leave a thawing pipe unattended. If it split, you want to be there when the water starts.
• Do not close the tap and walk away once you get a trickle. Let it run until the flow is normal.

If a pipe does let go, close the main shutoff at once. What to do in the hour after a burst is its own subject, and the first move is always the main valve.

Preventing frozen pipes in Ontario winters

London-area winters bring stretches of deep cold with wind, and many older homes in Old North, Wortley Village and Old East have plumbing running through outside walls and uninsulated crawlspaces. A few habits cover most of the risk.

• Before the first hard frost, disconnect garden hoses, close the inside shutoff for each outdoor tap and open the outdoor tap to drain it.
• Keep the house heated when you are away. Do not turn the thermostat right down to save on the gas or hydro bill.
• On the coldest nights, open cabinet doors under sinks on outside walls and let a thin stream of cold water run from the tap farthest from where the water enters the house.
• Seal gaps where cold air blows in around pipes, hose bibs and the rim joist, and insulate exposed pipes in crawlspaces and garages with foam sleeves.
• Keep the garage door closed if water lines run through the garage.
• If you go away in winter, have someone check the house regularly, or shut off the main and have the lines drained. Many insurance policies set conditions for homes left empty in the heating season, so read yours or ask your broker.

A leak sensor with an automatic shutoff valve on the main is worth considering for anyone who travels in winter. It cannot stop a pipe from freezing, but it closes the water when a split pipe starts to leak. For now, walk the house and find every pipe that runs along an outside wall, so you know where to look on the next cold night.

Common questions