Quick Answer:
If you see a visible fracture in the device body, shut the water off immediately, drain pressure, and prepare to replace the entire assembly. After replacement, make sure the installation is protected from freezing by insulating the enclosure and following simple winterization steps.
Why This Happens
Backflow preventers are exposed to cold and can hold water in small cavities. When that water freezes it expands and can crack the device body or internal chambers. Age, plastic parts, or repeated freeze cycles make the body more likely to fail. After a freeze you may also see leaks or pressure problems — for guidance on leak signs, see Backflow device leaking after winter.
Step-by-Step What to Do
1. Shut the water
- Close the nearest upstream isolation valve for the line served by the device. If that valve is not accessible, shut off the main water supply to the building.
- Open a downstream faucet to relieve pressure and drain water from the line so the device is empty.
- Do not try to operate or force the device while it is full of water and under pressure.
2. Confirm the visible fracture and assess damage
- With the water off and the device drained, inspect the body carefully. A hairline crack, split, or a clear fracture in the housing generally means the structural integrity is lost.
- Take photos for your records or to show a plumber or supplier.
3. Replace the assembly
- A fractured body almost always requires full replacement of the assembly rather than patching parts. Order the correct replacement model and spare parts, or have a plumber bring the correct unit.
- If you are comfortable with plumbing repairs you can replace it yourself following manufacturer instructions; otherwise hire a licensed professional. Make sure replacement uses correct fittings and test after installation.
4. Insulate the enclosure
- Install a well-fitting insulated box or cover around the device. Use closed-cell foam or an insulated enclosure designed for valves and backflow preventers.
- Where needed, add approved heat tape or a thermostatically controlled heater rated for wet locations — follow manufacturer instructions and local code for electrical connections.
- Ensure the enclosure remains accessible for testing and maintenance and that insulation does not trap moisture against the device.
5. Restore service and test
- Open the supply valve slowly while watching for leaks. Pressurize the line gradually.
- Confirm proper operation and check for any small drips. If you notice unusual flow behavior or suspect internal damage, turn water off and call a pro.
What Not to Do
- Do not wrap damaged body — wrapping a cracked housing with tape or cloth hides the problem and can fail dangerously when pressure returns.
- Do not patch a structural crack with glue, epoxy, or temporary tape and then pressurize the line.
- Do not use an open flame or high-heat tools to try to reshape or “melt” parts back together.
- Do not ignore a visible fracture and continue to run water through the device.
When to Call a Professional
- There is active leaking you cannot stop or isolate.
- You cannot access or shut off the correct isolation valve.
- The installation is part of a public water system connection and requires certified testing or a permit.
- You are unsure which replacement model fits your system or the repair requires soldering or electrical work for heat tape.
Safety Notes
- Always shut off and depressurize the line before touching the device.
- Wear gloves and eye protection when working with frozen or leaking assemblies — water and ice surfaces can be sharp.
- Follow electrical safety rules when installing heat tape or thermostats; turn off power before making connections if required.
- If you smell gas, detect a major leak, or encounter frozen pipes that may burst, evacuate and call emergency services as needed.
Common Homeowner Questions
- Can I repair a cracked backflow body? No — a cracked body should be replaced rather than patched.
- How soon can I turn the water back on after replacement? Turn it on slowly and check for leaks; if everything is tight you can restore service immediately.
- How do I check for other signs of failure? Look for reduced pressure, continuous leaks, or unusual flow patterns; for more detail see How to tell if backflow preventer failed.