Frozen Pipe Thaw and Damage Assessment
Purpose
Thawing a frozen line is the reversible half of this call. Putting the water back on is the irreversible half. Water expands roughly 9 percent when it freezes, and the split it causes almost never leaks while the ice is in place, so a tech who restores flow and drives away has handed the customer a pipe that opens minutes later with nobody home. This procedure closes the main before heat is applied, puts a person at the main when pressure is restored, and opens and watches every component that could hide a split.
Scope
Covers locating, thawing and post-thaw assessment of frozen potable water piping in a residential or light commercial building, on copper, PEX, CPVC or galvanized, including hose bibs and exposed runs in crawlspaces, attics and rim joist bays.
Does not cover frozen drain, waste or vent piping, frozen sprinkler systems, or buried service lines outside the building, which need utility coordination. Does not cover drying, contents or restoration; the sewage backup response and restoration handoff SOP owns that boundary. Does not cover the freeze prevention retrofit, quoted separately once this visit has found where the cold air was getting in.
Roles and responsibilities
| Role | What they own | The handoff |
|---|---|---|
| Dispatcher | Whether water is running anywhere, and whether the main is closed | Tells the customer to close the main before the truck arrives, and records whether they did |
| Technician | Isolation, the thaw, the pressurization, the damage record | Hands over only after step 9 has run on every fixture and bib, never on a pressure hold alone |
| Lead or owner | Opening any finished surface; partial isolation at handover | Approves the isolation plan in writing when a branch is capped rather than repaired |
| Office | Getting the damage record to the customer the same day | Sends it without interpreting it; the shop states what it found, the insurer decides coverage |
Procedure
De-energize and prove dead the circuits serving any space with standing water. Open the breakers feeding the area and verify absence of voltage on a tester proved live before and after. Acceptance: no voltage at the affected receptacles and lighting circuits. Wrong looks like reaching for a light switch while standing in an inch of water. Stop rule: if the panel is across the water, do not cross; have the utility or an electrician isolate it. Hazard: water plus energized conductors, controlled by 29 CFR 1910.333(b)(2) since 1910.147 excludes electrical utilization work at (a)(1)(ii)(C); live-dead-live proving is NFPA 70E-2021, 120.5.
Close the main and prove the system dead before any heat touches any pipe. Close the main, open a low fixture and a high one. Acceptance: the low fixture stops rather than trickling, and a gauge at a bib reads zero. Wrong looks like thawing with the water on, which turns a wall-cavity split into a ceiling on the floor. Stop rule: if the main will not close fully, isolate at the curb stop or call the utility; never thaw a line under pressure. Hazard: heat with the main open puts full system pressure behind a pipe you know is overstressed.
Fix the heat source before you start. No open flame, on any material, in any location. Acceptance: heat only from a heat gun on low kept moving, a hair dryer, a pipe-rated heat cable, warm wet towels or an electric space heater, named on the ticket. Wrong looks like a torch on copper in a joist bay, igniting framing you cannot see. Stop rule: if the spot cannot be reached by an allowed source, open access rather than reach for a flame. Hazard: a fuel-fired salamander or propane heater produces carbon monoxide in an unventilated crawlspace or basement, so neither is permitted indoors, and any tech in an enclosed space wears a personal CO monitor.
Map the extent before you go looking for the plug. Open every fixture, hot and cold, and record which flow, which trickle, and which give nothing. Acceptance: a fixture-by-fixture map on the ticket. Wrong looks like chasing the one fixture the customer named, finding one plug in a building that has three. Stop rule: dead fixtures on separate branches mean the freeze is upstream of the branch point, so warm the whole building rather than spot-thaw. Hazard: leave the opened fixtures open; they are the escape path for meltwater and expanding air.
Find the plug by following the cold, not by guessing. Run a hand or infrared thermometer along accessible pipe from a working fixture toward the dead one; the plug is where the pipe goes cold and stays cold. Acceptance: a located cold section, or a suspect location backed by a visible cause such as an open rim joist penetration. Wrong looks like an assumed location that opens the wrong wall. Stop rule: if the run is concealed and you cannot locate it, warm the whole space rather than cut finished surfaces on a guess, and escalate the open-a-wall call to the lead. Hazard: check the attic or crawlspace access for ice, and never enter a crawlspace without someone outside knowing.
Thaw from the open fixture end toward the plug, never the middle, and stay inside the pipe's temperature limit. Start nearest the open fixture and work back toward the frozen section, source moving. Acceptance: water runs at the fixture, first a trickle then steadily, with heat still applied between fixture and ice, and no gloss change or deformation on the pipe. Wrong looks like starting mid-plug, melting water trapped between two ice masses with nowhere to expand, or a gun held stationary on CPVC or PEX, which distorts the wall and fails days later. Stop rule: PEX to ASTM F876 is rated 200 F at 80 psi, 180 F at 100 psi and 73.4 F at 160 psi, so any softening or deformation means stop, cool it and replace that section; and if flow does not begin with the pipe warm both sides of the plug, move the search rather than add heat. Hazard: the gun's outlet and the heated pipe burn on contact, and copper conducts heat into the framing, insulation or vapor barrier it is clipped to, so shield combustibles and keep bare hands off.
Confirm the plug is fully cleared, not just partly opened. Acceptance: full steady flow matching a known good fixture on the same branch, sustained at least a minute. Wrong looks like a restored trickle, meaning ice is still in the line and the section is still a closed pocket. Stop rule: partial flow is not a completed thaw, so keep heating and do not pressurize; system pressure onto a remaining plug is how the split opens. Hazard: leave the fixture open and keep the space warm, because a section thawed once in a cavity still admitting outside air refreezes overnight.
Restore pressure slowly with a person at the main and eyes on the pipe. Crack the main partway, one tech at the valve, another walking the accessible runs, gauge on a bib. Acceptance: pressure reaches the building's normal static and holds 15 minutes with every fixture closed, no drop on the gauge. Wrong looks like opening the main fully and going to write the ticket. Stop rule: any drop on a closed system, or running water heard with no fixture open, means close the main and find it. Hazard: the first pressurization is when the split opens, so nobody stands under a ceiling below a suspect run.
Open every fixture and hose bib individually; a static hold does not test what sits behind a closed seat. Acceptance: every fixture and exterior bib operated in turn, someone watching the wall or ceiling behind each bib. Wrong looks like signing off on a clean 15 minute hold. A frost-free sillcock splits at its inboard end inside the wall, downstream of its own seat, so it sees no pressure until the handle is turned. Stop rule: a bib that sprays into a cavity gets its branch isolated or capped, the main closed, and the wall opening escalated to the lead. Hazard: a split component sprays at full system pressure toward whoever opened it, so stand to the side.
Record the damage and the cause, then secure the building. Photograph every split component, every wet surface, and the entry point where cold air reached the pipe. Acceptance: photographs, a list of affected fixtures, the freeze point, the named cold air path, and the isolation state at handover. Wrong looks like a ticket reading "thawed pipe, restored service" where a wall is open and a branch is capped. Stop rule: on partial isolation the customer signs for that state and the record names which fixtures are out of service. Hazard: insulation over a pipe still bathed in outside air makes the next freeze likelier, so the record names the air leak, not just the pipe.
The record this produces
Ten fields: whether the main was closed on arrival and by whom, which circuits were isolated, the fixture map from step 4, the freeze point, the heat source used, the pipe material and whether any section was heat-affected, the step 8 hold result with pressure and duration, the step 9 per-bib result, every split component found, and the isolation state at handover, with photographs attached to the job.
They land on the job and the property record. The insurer reads the split list, freeze point and photographs, and a dated plumber's record moves a claim faster than a homeowner's description. The next tech reads the isolation state; the estimator reads the cold air path, which is the prevention scope.
One worked pass, including a failure
Unoccupied vacation house, three nights near 5 F outside, thermostat at 50 F but the furnace locked out. No water at two second-floor fixtures and the kitchen sink; the main untouched.
Basement dry, affected circuits opened at the panel anyway (step 1). Main closed, low laundry bib open, gauge zero within a minute (step 2). Heat gun on low plus an electric space heater, no fuel-fired heater (step 3). The map shows the cold side dead at the kitchen and both second-floor fixtures, the hot side and the laundry cold line fine, so one cold branch rather than a whole-building freeze (step 4). Following the cold finds the kitchen branch crossing an open rim joist bay where a dryer vent penetration was never sealed, copper at outside temperature (step 5). Heat started at the kitchen end and worked back with the faucet open, gun moving, no deformation on the copper: trickle at about 20 minutes, full steady flow matching the laundry bib at about 40 minutes, held a minute (steps 6 and 7).
Step 8: main cracked open, tech at the valve, gauge on the laundry bib. Pressure reaches 58 psi and holds 58 psi for the full 15 minutes with every fixture closed, so on a static test this building looks clean.
Step 9 fails. Working the exterior bibs in turn, the front frost-free sillcock sprays inside the wall cavity the moment it is opened, audible through the drywall. This is what step 8 cannot catch: the split sits inboard of the seat and saw zero pressure during the hold. Stop rule taken - main closed, that branch isolated at its shutoff, wall opening escalated to the lead.
Step 10 records it: three affected fixtures, freeze at the unsealed rim joist penetration, one split component (front sillcock, inboard of the seat), no ceiling damage, furnace locked out, branch left isolated and signed for. The prevention quote seals the penetration, not the pipe.
Three sites do not match this procedure. Water already restored, building wet: a damage assessment, not a thaw - close the main, run steps 8 through 10, hand off with a written boundary. Pipe visibly split while still frozen: cut it out cold, or thaw with the branch isolated and a container under it, and replace before any pressurization. No heat and none coming today: leave the main closed and drain the system down, because a drained building has no further damage available to it.
References
- 29 CFR 1910.333(b)(2) for the electrical safe work practice, with the 1910.147(a)(1)(ii)(C) carve-out that sends electrical utilization work there, and 29 CFR 1926.417 as the construction counterpart.
- NFPA 70E-2021, 120.5, for the live-dead-live proving sequence in step 1.
- ASTM F876 for the PEX ratings in step 6, plus heat gun, heat cable and pipe manufacturer literature for CPVC and PE-RT limits, surface temperature and approved materials.
- See related: the Plumbing sewage backup response and restoration handoff SOP, for the written boundary when handing a wet building to a restoration contractor.