Why do frozen pipes burst when they thaw?
The split usually happens during the freeze, not the thaw. Ice seals it shut, so nothing escapes. When the plug melts, pressure returns to a pipe that already has a hole in it, and the water finds the break immediately.
This single mechanism explains the timing of almost every freeze call we take. The homeowner reports the leak starting suddenly on a mild afternoon, and it did — but the damage was done a day or two earlier in the cold.
What actually splits the pipe?
Not ice pressing outward on the pipe wall. Ice forms a plug, then water trapped between that plug and a closed fixture is compressed as the ice keeps growing. The pipe fails at its weakest point, which is often well away from the frozen section.
It follows that the split is not necessarily where the pipe was coldest, and that leaving a tap cracked open genuinely helps — it relieves the trapped pressure rather than keeping the pipe warm.
How do I know if my pipes are frozen?
No water or a trickle at one or more fixtures on a cold morning, while other fixtures run normally. Frost or condensation on an exposed pipe. A section of pipe noticeably colder than the rest of the run.
- A tap that gives a trickle then nothing, with other taps working
- No water at all on the coldest morning of the month
- Visible frost on an exposed crawlspace or garage run
- Bulging or deformation on a pipe you can see
If it is only one fixture, the freeze is in that branch. If nothing in the house runs, it is upstream — possibly the buried run between the meter and the building, which on larger Bend lots can be long.
Should I call before or after it thaws?
Before. While the pipe is still frozen you have the cheap outcome available: a controlled thaw with the section isolated and someone watching it come back up to pressure. After the thaw you are paying for a repair plus drying out a wall.
That window is the whole reason this page exists. "No water this morning" is worth a call. Waiting to see whether it sorts itself out converts a small job into a large one, and you will not know which you have until the water arrives.
We take frozen pipe repair calls across Bend through the winter and would rather thaw a line than replace one.
Can frozen pipes thaw on their own?
Yes, and that is exactly the problem. An unattended thaw is how a split pipe empties into a building with nobody there. If a line has frozen, it needs to be thawed under supervision with the main shutoff within reach.
Never use an open flame. A heat gun or torch on a frozen pipe risks igniting framing and can damage the pipe itself. Gentle, even warmth applied from the fixture end toward the frozen section is the approach — and the main shutoff stays accessible the whole time.
What does the repair cost if it has already split?
A controlled thaw with no rupture typically runs $150 to $450. An accessible section repair runs $350 to $900. In-wall or in-ceiling work runs $600 to $1,800, because opening and closing the access is most of the labour.
Those figures are why the timing question matters so much. Calling while the line is frozen and calling after it has emptied into a wall are separated by roughly an order of magnitude, and the decision is usually made by someone who did not know there was a decision to make.
If it has already gone, burst pipe repair is the page with the full detail — including when a run that has failed once should be repiped rather than patched again.
Last reviewed 2026-09-21 by Bend Plumbing Pros, Bend, OR.