Runs in an exterior wall cavity
Insulation is usually behind the pipe rather than in front of it, so the run sits between the cold sheathing and a warm room it cannot reach.
Frozen pipe repair in King City, CA, thawed carefully and then corrected so it does not repeat
A run that froze once will freeze again next winter unless the insulation, the routing or the heat reaching it changes.
A frozen pipe is two problems arriving together. The first is immediate: no water at a fixture, and a section of pipe containing an expanding plug of ice that may already have split the wall without anybody knowing. The second is that the split will not announce itself until the ice melts, which is frequently hours after the thaw, often overnight, and usually while nobody is watching.
That second problem is why thawing carelessly is worse than not thawing at all. Warming the whole run quickly releases the blockage and any water behind it at once, into whatever damage the ice has already done. Controlled thawing means working from the fixture end back toward the blockage so meltwater has somewhere to go, and being present when flow returns.
What to do before anyone arrives
Four actions that make a large difference to how a freeze ends.
Open the fixture served by the frozen run, both hot and cold. This does two things: it relieves pressure building between the ice plug and the closed tap, which is what actually splits pipes, and it gives you an immediate signal when the blockage clears. A trickle appearing at an open tap tells you the thaw is working before anything dramatic happens.
Find the main shut off and confirm it turns. If a section has already split, the moment the ice releases is the moment water starts escaping, and the difference between reaching the valve in ten seconds and hunting for it for five minutes is substantial. This is worth doing on a calm afternoon rather than during the event.
Do not use an open flame. Blowtorches on frozen pipes cause structure fires, and they do it regularly enough that it is one of the most consistent pieces of advice in the trade. They also heat unevenly, which can flash trapped water to steam and burst a pipe that the ice had not yet damaged. Warm air, heat tape designed for the purpose, or simply raising the temperature of the space are all appropriate.
Raise the temperature around the run if you can, and open any cabinet doors that enclose pipework on an exterior wall. A vanity or a sink base cabinet isolates the plumbing inside it from the heated room, and opening the doors is frequently enough to prevent a freeze or to assist a slow thaw.
Before the visit
Four things worth doing immediately, all of which reduce the eventual damage.
- Open the affected fixture, hot and cold, to relieve pressure and signal the thaw
- Locate the main shut off valve and confirm that it actually turns
- Keep flames away from the pipework, without exception
- Open enclosed cabinets and raise the temperature around the run
Where freezes happen and why
Six locations that account for most frozen runs, and what makes each vulnerable.
Freezes are highly predictable in their locations. They happen where a pipe is exposed to cold and isolated from building heat, and the same handful of situations turn up in building after building.
Knowing which applies to your property is what makes prevention possible rather than hopeful.
Crawl space and underfloor runs
Vented crawl spaces reach outdoor temperature. Pipes there depend entirely on their own insulation and on any heat leaking through the floor.
Garage and unheated utility spaces
A water heater or a laundry connection in an attached garage is at ambient temperature the moment the door is left open on a cold night.
Runs above an unheated porch or bay
The floor cavity over an unheated projection is effectively outside, and the pipes crossing it are frequently uninsulated.
Hose bibs and external supply
A bib left connected to a hose cannot drain, so water sits in the wall section behind it and freezes there rather than outside.
Anywhere a draft reaches the pipe
A gap at a rim joist or a service penetration channels cold air directly onto a run that would otherwise be fine.
How the call is handled
Six steps, with the split found before the water arrives rather than after.
The order is designed around the fact that the damage is usually invisible until the thaw completes. Finding it first is far better than discovering it when flow returns.
Isolate and assess
Main shut off located and operated, the affected run traced, and the likely frozen section identified from the layout and the exposure.
Inspect before thawing
The accessible length examined for bulging, splits and deformation, so any damage is known before water is allowed to reach it.
Controlled thaw
Warmth applied from the open fixture end back toward the blockage, gradually, with the fixture open so meltwater escapes as it forms.
Watch the flow return
Somebody is present when the plug releases, which is the moment any split will make itself known, with the shut off already in hand.
Cut out and replace
Any damaged section removed and replaced properly rather than patched, and the surrounding length checked for less obvious deformation.
Correct the exposure
Insulation, heat tape, rerouting or sealing the air path that caused it, so the same run is not a repeat call next winter.
Preventing the next one
The repair fixes the pipe. Correcting the exposure is what stops the annual call, and it is usually inexpensive.
Pipe insulation is the obvious measure and it is frequently misunderstood. Insulation does not add heat, it slows the loss of it, which means it delays a freeze rather than preventing one. On a run that gets some heat from the building, insulation is enough. On a run in a genuinely unheated space during a prolonged cold spell, insulation alone only buys time.
Where heat is genuinely absent, self regulating heat cable is the answer. It runs along the pipe under the insulation and draws power in proportion to how cold it is, which means it costs very little in mild weather and works when needed. Fitted correctly with a proper supply it is reliable, and it is the right solution for crawl spaces, garages and any run that has frozen before despite being insulated.
Air sealing is the underrated one. A great many freezes happen because cold air is being channelled directly onto a pipe through a gap at a rim joist, a service penetration or a poorly fitted vent. Sealing that path costs very little and frequently solves the problem outright, because the pipe was never short of heat, it was being actively cooled by a draft.
Rerouting is the last resort and occasionally the only real answer. A run that passes through a genuinely hostile location, such as the floor cavity above an unheated porch, may be better moved than protected. That is a larger job and it is presented as an option rather than a requirement, with the cost against the likelihood of it happening again.
Measures in order of cost
- Seal the air path channelling cold onto the run, often the whole fix
- Insulate the pipe properly, including the awkward sections nobody reaches
- Open enclosed cabinets on exterior walls during cold spells
- Fit self regulating heat cable where the space is genuinely unheated
- Reroute the run where the location cannot be made survivable
Frozen pipe questions
Thawing safely, whether a pipe has split, prevention and what to do when leaving a property empty.
Carefully, and only with warm air or an appropriate heating device. Never with a flame. Work from the open fixture end back toward the blockage so meltwater has somewhere to escape, and stay with it.
The reason to be present is that the moment the plug clears is the moment any split starts leaking. If you are not there with the shut off within reach, a successful thaw becomes a flood.
You often do not until it thaws, which is the difficult part. Visible bulging or a section that looks deformed is a clear indicator, but plenty of splits are hairline and invisible until pressure returns.
That is why the inspection happens before thawing where the run is accessible, and why somebody stays with it as flow returns rather than warming it up and walking away.
Sometimes, and not always. Insulation slows heat loss rather than adding heat, so on a run that receives some warmth from the building it is enough. On a run in a genuinely unheated space during a long cold spell it only delays the freeze.
Where a pipe has frozen despite being insulated, the answer is usually either sealing a draft that is cooling it or fitting self regulating heat cable. Both are inexpensive compared with the repair.
For a run that is known to be vulnerable, yes, and it is a reasonable short term measure during a severe cold spell. Moving water freezes more slowly and a slightly open tap also relieves the pressure that actually splits pipes.
It is a stopgap rather than a solution. A run that needs a dripping tap every winter needs the underlying exposure dealt with.
Do not switch the heating off entirely. Leave it at a low setting rather than off, open cabinet doors enclosing pipework on exterior walls, and if the property will be empty for an extended period, have the system drained down properly.
Where somebody can check the building periodically, that is worth arranging. A split discovered on day two is a repair, and the same split discovered on day thirty is something else entirely.
Because a hose left connected over winter stops the bib draining. Water sits in the section behind the wall where it is warmer than outside but still below freezing, and that is where it splits.
Disconnecting hoses in autumn prevents it. Frost proof bibs help considerably and only work when nothing is attached to them, which is the detail that catches people out.
No water, or a run you think has frozen
Attended around the clock in King City, CA, with the exposure corrected afterwards rather than just the pipe.
Open the affected tap, locate your main shut off, and keep any flame away from the pipework. Those three things matter more to the outcome than how fast anybody can get there.
Tell the desk which fixtures have no water and roughly where the run passes if you know. That narrows the frozen section considerably before anyone arrives.
Around the clockFreeze calls attended out of hours
Inspected firstSplits found before water is allowed back
ReplacedDamaged sections cut out, not patched
CorrectedThe exposure addressed so it does not repeat