Use of electric heating cable is a good method of thawing frozen pipe,
because the entire heated length of the pipe is thawed at one time.
Thawing pipe with a blowtorch can be dangerous. The water may get hot
enough at the point where the torch is applied to generate sufficient
steam under pressure to rupture the pipe. Steam from the break could
severely scald you.
Thawing pipe with hot water is safer than thawing with a blowtorch.
One method is to cover the pipe with rags and then pour the hot water
over the rags.
When thawing pipe with a blowtorch, hot water, or similar methods, open
a faucet and start thawing at that point. The open faucet will permit
steam to escape, thus reducing the chance of the buildup of dangerous
pressure. Do not allow the steam to condense and refreeze before it
reaches the faucet.
Underground metal pipes can be thawed by passing a low-voltage electric
current through them. The current will heat the entire length of pipe
through which it passes. Both ends of the pipe must be open to prevent
the buildup of steam pressure.
CAUTION: This method of thawing frozen pipe can be dangerous and should
be done by an experienced person only. It cannot be used to thaw
plastic tubing or other non-electricity-conducting pipe or tubing.