Pipes burst from freezing, high water pressure, corrosion and age, a failed fitting, tree roots or shifting ground, and water hammer. In cold weather, expanding ice does it. In warm weather, pressure and wear do. Many Los Angeles bursts trace to pressure and old pipe rather than frost. The sections below take each cause in turn and end with a prevention checklist you can use this week. For the wider picture of leak work, see our page on a plumber for leaks.
What are the main reasons a pipe bursts?
The main reasons are freezing, excess pressure, corrosion, age, physical damage, and sudden pressure swings such as water hammer. A pipe fails where it is weakest: a thin spot, a fitting or a joint. Several causes often combine, such as old pipe under high pressure.
Freezing. Water expands about 9 percent when it turns to ice. Plumbing industry sources say a pipe often bursts as the ice thaws and pressure is released, not while it is frozen.
High pressure. Constant pressure above what the plumbing is designed for strains fittings, supply lines and hoses.
Corrosion. Pipe walls thin from the inside or outside until a pinhole or split opens.
Age and material. Some materials wear out, and some products were later found to fail early.
Damage and movement. A nail through a pipe, a digging mistake, tree roots or ground movement can break one in a moment.
Pressure surges. Quick valve closing sends a shock through the line, and a stuck regulator can let full street pressure in.
Why do pipes burst in winter?
Water inside a pipe freezes, expands about 9 percent and builds pressure between the ice plug and a closed faucet. The pipe then splits, usually when the ice thaws and water flows. Industry sources put the risk point near 20 degrees Fahrenheit or lower, held for hours, with attic and crawl space pipes most exposed.
Freezing is less common in Los Angeles than in cold states, but foothill and valley nights can get cold, and a wind can blow into an unheated space. Pipes on exterior walls, in attics, in garages and outside are the first to go. A hose bib left connected can freeze and push ice back into the wall.
If you have a frozen pipe, shut off the water to it and call a plumber before you thaw it. Our guide to emergency help for a burst pipe covers the steps.
What causes a pipe to burst in summer?
In warm weather, bursts come from high water pressure, thermal expansion, corrosion, failed fittings and ground movement. Freezing is not the cause. Heat can speed up wear on old plastic and rubber, and hot water heating inside a closed system raises pressure if there is no place for it to expand.
A water heater is a closed system when a check valve or pressure regulator sits on the supply. As water heats, it expands, and with no expansion tank pressure can spike and stress pipes, fittings and the relief valve. See replacing a water heater expansion tank for that fix.
A banging pipe is a clue. If you hear a bang when a valve closes, read about water hammer sounds, because repeated shocks wear joints.
Can high water pressure burst a pipe?
Yes, if it is high enough or constant. The California Plumbing Code requires a pressure regulator when static pressure at the building exceeds 80 psi. Pressure varies by street and elevation, so a home low in a hilly area can see more than one higher up. A gauge on an outdoor spigot tells you.
Signs of high pressure include banging pipes, a relief valve that drips, short-lived faucets and hoses that burst. A pressure regulator can stick open or wear out, which lets full street pressure into the house. A plumber tests it with a gauge and replaces the valve if needed.
You can buy a screw-on gauge at a hardware store and test the pressure at a hose bib. Our guides on the water pressure regulator and why water pressure is low show the other side of the scale. The point is not to assume that either too low or too high is normal.
How do corrosion and old pipe cause bursts?
Pipe wears out from inside and outside. Water chemistry, oxygen and flow can eat at metal, while soil, moisture and fittings can corrode it from the outside. Wall thickness drops until a pinhole forms, and one pinhole often signals more on the same line. Old galvanized steel also rusts and narrows.
How long pipe lasts depends on the material, the water and the installation, so no single date applies. If you have repeated leaks on one line, or the pipe is old, a plumber may recommend replacing it. See galvanized pipe replacement and repiping a house for that decision, and polybutylene pipe replacement if your home has that grey plastic pipe.
Pinhole leaks in copper are a common warning. Our guide to fixing a pinhole leak in copper pipe shows temporary measures, and a plumber can judge the rest of the line.
How can you prevent a pipe from bursting?
Know where your main shutoff is and test it, check your water pressure, insulate exposed pipe, replace old supply hoses and fix small leaks before they grow. A little work lowers the odds, and a quick shutoff limits the damage when one still fails.
A short checklist:
- Turn the main valve once a year so it does not seize.
- Check water pressure with a gauge. Over 80 psi needs a regulator.
- Replace rubber washing machine hoses with braided ones and inspect them regularly.
- Insulate pipes in attics, garages and crawl spaces.
- Disconnect garden hoses, and cover or drain outdoor lines before a cold spell.
- Watch your meter and your bill for unexplained changes. The US EPA suggests a two-hour meter test.
- Do not ignore stains or damp spots.
For signs of a burst already under way, see how to know if a pipe burst. If you want a plumber to check pressure, valves and old lines, send your details through our quote page and we arrange a visit.
Common questions
How long does a plumber take to fix a burst pipe?
An accessible pipe is often fixed in a few hours. A pipe in a wall adds time to open and close the wall, and one under a slab can take a day or more. Fixing the cause, such as high pressure or old pipe, may be extra work. Ask for the plan and timing in the written quote.
What should I ask a plumber about the cause of a burst?
Ask what failed and why, whether the pressure was tested, whether the rest of the pipe is in similar shape and what would stop it happening again. A good plumber shows you the damaged section. For jobs of $1,000 or more, check their state license on the CSLB website before you agree.
Does someone need to be at the property?
Yes for the first visit, so the plumber can see the main valve, the pressure gauge point, the water heater and any trouble spots. A pressure test or valve check is quick. If a repair is needed, someone responsible should be home while the water is off. Tell the plumber where hoses and outdoor lines run.
Does cold weather in Los Angeles ever burst pipes?
It can, though less often than in cold states. Industry sources put the freezing risk at around 20 degrees Fahrenheit or lower for several hours, and pipes in attics, garages and outside walls are most exposed. Insulating exposed pipe and disconnecting hoses before a cold night is cheap protection.
Can a pipe burst without a cause I can see?
Yes. Corrosion, a fitting weakness or a pressure surge often leaves no outside clue until the pipe fails. That is why a plumber looks at pressure, age and material after a burst, rather than only fixing the split. If one pipe failed, others of the same age may be close behind.