What to Do When a Pipe Freezes or Bursts: Step-by-Step Guide

A frozen or burst pipe is one of the most stressful plumbing emergencies an Ontario homeowner can face — and with winters regularly pushing temperatures below -20°C across the GTA, Brampton, Vaughan, and Mississauga, it is a real and present risk every year. Acting quickly and correctly in the first few minutes can be the difference between a minor inconvenience and tens of thousands of dollars in structural water damage. This guide walks you through every step, from the immediate emergency response to long-term prevention.

Step 1: Locate and Shut Off Your Main Water Valve

The single most important thing you can do when you suspect a burst pipe — or even a frozen pipe that might burst — is to immediately locate and close your main water shut-off valve. Every resident in the home should know where this is before an emergency occurs.

In the vast majority of Ontario homes, the main shut-off valve is located in the basement, near where the municipal water line enters the house — typically along the front foundation wall or in the mechanical or utility room. In newer homes built after the mid-1990s, you will likely find a ball valve (a lever handle that turns 90 degrees to shut off flow). In older homes, a gate valve (a round wheel you turn multiple times clockwise) is common.

In condominium or townhouse units, check the mechanical room on your floor, or the area near your unit's water meter if one is present. Many older apartment buildings have shut-offs inside the unit under the kitchen sink or in a utility closet.

Once you have located the valve, closing it stops all water supply to the home. Do this immediately if:

• You can see water actively spraying or pooling from a wall, ceiling, or floor
• You turn on a tap and nothing comes out during a cold snap (frozen pipe — shut off before thawing to reduce burst risk)
• You hear a hissing or rushing sound inside a wall
• A section of drywall, ceiling, or flooring is visibly bulging with water

Frozen Pipe vs. Burst Pipe: Understanding the Difference

A frozen pipe means ice has formed inside the pipe, blocking or significantly restricting water flow. The pipe itself may still be structurally intact. You might notice this when a faucet produces only a trickle or nothing at all during or after a cold spell, despite the main water supply being on.

A burst pipe means the expanding ice has caused the pipe to crack or rupture. This is the dangerous scenario. Copper and CPVC (chlorinated polyvinyl chloride) pipes are rigid and have no ability to flex under ice pressure — when ice expands, the pipe gives way. PEX (cross-linked polyethylene) flexible tubing, which is increasingly common in newer Ontario homes, handles freezing better because it can flex slightly, though it can still fail under severe conditions.

How to Safely Thaw a Frozen Pipe

Once you have shut off the main water supply and confirmed the affected pipe has not yet burst, you can attempt to thaw it. The goal is to apply gentle, even heat starting at the faucet end and working backward toward the frozen section. This allows steam and water to escape as the ice melts.

Approved Thawing Methods

• Hair dryer (lowest setting): The most practical household tool. Hold it 15–20 cm from the pipe and move it slowly along the frozen section. This method works well for exposed pipes under sinks, in utility rooms, or in crawl spaces.
• Warm, wet towels: Soak towels in warm (not boiling) water and wrap them around the frozen section. Replace as they cool. This is slow but very safe for pipes near finished drywall.
• Electric pipe heating cable: Pre-installed or wrap-around heating cables designed for pipes are effective and safe when used per manufacturer instructions. They are particularly good for ongoing protection in problem areas.
• Portable space heater (at a distance): Directing a portable electric heater toward an exposed frozen pipe section can work but requires careful monitoring and should never be left unattended near combustible materials.

What Never to Do

• Never use an open flame — propane torch, butane lighter, or heat gun. This is a fire hazard and can cause the pipe to burst from rapid uneven heating.
• Never pour boiling water directly onto a pipe or fitting. The thermal shock can crack copper and damage solder joints.
• Never use a heat gun set to high — the concentrated intense heat replicates the risks of an open flame.

What Causes Pipes to Freeze in Ontario Winters

Ontario winters are unforgiving. The GTA experiences multiple sub-zero cold snaps each season, and during polar vortex events, temperatures can plunge to -25°C or colder with wind chills pushing the effective temperature even further below zero. Pipes freeze when the ambient temperature around the pipe drops below approximately -6°C (21°F) — though this threshold can be lower for well-insulated pipes and can be reached faster by pipes exposed to wind chill through air leaks in the building envelope.

The Primary Risk Factors

• Pipes in exterior walls: The most common culprit in Toronto-area homes. Pipes routed through exterior walls — particularly older homes where plumbing was retrofitted — have only the wall's insulation separating them from outdoor temperatures. Many Ontario homes built before the 1970s have inadequate wall insulation by modern standards.
• Unheated or poorly heated spaces: Garages (especially attached garages with water supply lines for laundry or utility sinks), crawl spaces, attics, and mechanical rooms that lose heat quickly are high-risk zones.
• Pipes near air leaks: Even a small gap around a dryer vent, electrical conduit, or pipe penetration through an exterior wall can expose nearby pipes to wind chill temperatures that are dramatically colder than the room's ambient temperature.
• Hose bibs (outdoor taps): Unless you have frost-free hose bibs — which are standard in newer Ontario construction — the supply line to outdoor taps can freeze and burst if the interior shut-off valve is not closed and the line drained before winter.
• Vacant homes during cold snaps: If you leave your home for the holidays or an extended period during an Ontario winter and the heat is set too low (below 13°C) or fails while you are away, an entire home's plumbing can freeze.

Which Pipes Are Most Vulnerable

Not all pipes carry the same freeze risk. Understanding your home's plumbing material can help you prioritize preventive action. Homes in Toronto, Mississauga, and Brampton built in different eras typically have different pipe materials:

• Copper pipe (common in homes built from the 1950s through the 1990s): Rigid, conducts cold rapidly, and has no flex tolerance when ice expands. High burst risk.
• CPVC (cream-coloured plastic) (common in homes from the 1980s–2000s): Similarly rigid. Can crack cleanly when frozen, making it somewhat easier to detect the damage.
• Galvanized steel (found in pre-1960s homes): Already prone to corrosion and scale buildup, which narrows the pipe's interior. Frozen galvanized pipe in older Etobicoke or East York homes, for example, is a compound problem.
• PEX tubing (standard in new builds post-2000): Has excellent freeze tolerance due to its flexibility, but is not immune — extreme cold or prolonged exposure can still cause failure.

Supply lines to fixtures — the braided steel or plastic lines connecting shut-off valves under sinks to faucets — are also vulnerable in unheated cabinets on exterior walls.

What to Do After a Burst Pipe

If a pipe has already burst and water is actively leaking, the sequence of actions matters enormously for minimizing damage.

1. Shut the main water valve immediately. Review Step 1 above if you have not already done this.
2. Turn off electricity to affected areas if water is near electrical outlets, panels, or fixtures. Do this at the breaker panel. Water and electricity are a life-threatening combination.
3. Open all taps in the home to drain remaining water from the pipes and reduce pressure.
4. Begin water extraction and drying immediately. Use towels, mops, wet/dry vacuums. Remove standing water from hardwood, engineered wood, or laminate flooring within the first few hours to prevent permanent warping and mould growth.
5. Call a licensed plumber. Burst pipe repair is not a DIY job — it requires identifying the extent of the damage, cutting out the compromised section, and properly joining new pipe. In Ontario, work on pressurized water supply lines should be done by a licensed plumber. Contact Mechora Group's pipe repair team for the GTA.
6. Document all damage thoroughly. Take photos and video of every affected area before you begin cleanup. Note the date and time.
7. Contact your home insurer. Most standard Ontario home insurance policies cover sudden and accidental water damage from a burst pipe. Call your insurer's claims line and follow their instructions — they may require an adjuster to visit before major repairs begin.

For emergency plumbing situations across the GTA, Mechora Group Inc. can assess the damage and begin repairs. Do not delay — every hour that water remains in contact with wood, drywall, and insulation increases the risk of mould.

How to Prevent Frozen Pipes: Ontario Winter Strategies

Prevention is far less expensive than remediation. Here are the practical steps that matter most for Ontario homes:

Insulation

Pipe insulation sleeves — foam tubes available at any hardware store — are inexpensive and highly effective for exposed pipes in utility rooms, crawl spaces, garages, and under kitchen sink cabinets on exterior walls. They add a thermal buffer that significantly slows heat loss from the pipe to the surrounding cold air.

For pipes inside exterior walls, adding proper building insulation is a more involved renovation project, but it is the permanent fix. A licensed contractor or insulation specialist can assess your wall assembly and recommend the right approach. This is particularly relevant for Toronto homes built before 1970 that have not been renovated.

Heat Tape and Heating Cables

Self-regulating electric heat tape wraps around vulnerable pipe sections and automatically adjusts its heat output based on ambient temperature. It is especially useful for pipes in garages, crawl spaces, or areas that cannot be effectively insulated. CSA-approved products are available at hardware stores. Always follow the manufacturer's installation instructions and never overlap heat tape on itself.

The Drip Method for Extreme Cold

During a severe cold snap — Environment Canada polar vortex advisories are a good trigger — allow the cold-side faucet of any sink served by a vulnerable exterior-wall pipe to drip slowly. Moving water is significantly harder to freeze than static water. The minimal water consumption cost is trivial compared to the risk of a burst pipe.

Keep Your Heat On

When leaving your home for an extended period in winter, never set the thermostat below 13°C (55°F). This maintains enough ambient warmth throughout the home to prevent pipes in interior spaces from freezing, even during severe cold snaps. Consider a smart thermostat that allows remote monitoring and adjustment.

Disconnect Garden Hoses and Shut Off Hose Bibs

Every fall before freeze-up, disconnect all garden hoses from exterior taps. If your hose bibs are not frost-free models, locate the interior shut-off valve for each hose bib, close it, and open the exterior tap to drain the line. This prevents the classic burst hose-bib scenario.

For homes in Mississauga, Brampton, and Vaughan where attached garages are common, the water supply line to a utility sink or laundry connection in the garage is a critical pipe to insulate — garage temperatures can drop to outdoor levels quickly, especially in an uninsulated or poorly insulated garage.

When to Call an Emergency Plumber Immediately

Some situations require professional intervention without delay. Call a licensed plumber immediately if:

• Water is actively flowing from a burst pipe and you cannot locate or close the main shut-off valve
• You smell a musty or sewage odour combined with water damage (this may indicate drain pipe involvement)
• The affected pipe is inside a wall you cannot access without cutting drywall
• The burst is near your electrical panel, outlets, or any wiring
• You have thawed a frozen pipe but still have no water pressure at that fixture (the pipe may have burst in a section not yet visible)
• Multiple areas of the home have frozen — this suggests a systemic problem that requires professional assessment

Mechora Group Inc. is Licensed & Insured, serving the Greater Toronto Area. Our emergency plumbing service covers Toronto, Mississauga, Brampton, Vaughan, Markham, and Oakville. Call (249) 733-7907 or visit our contact page to request urgent service.

Also see our related guide: Residential Pipe Repair Services for information on what a professional pipe repair involves.