I believe I have a frozen pipe in my master bath. The water in the whole house runs fine... and even the cold water to the master bath sink works. It is only the hot water tap in the sink that doesn't work... not even a trickle. I've tried a bliw dryer but the pipe goes into the wall - an outside wall - and nothing seems to help. Ideas? Do I need to panic and call a plumber at midnight? Or just open the cabinet door, leave the taps open a bit, close the bathroom door, crank the heat, and hope for the best?

Open the cabinet door to let heat in. Leave lights on. If possible put a light with 60w blub in the cabinet. That will generate some heat. No need to call plumber unless pipe burst and you won't know that until it thaws.

I had a call last winter where pipe only froze on cold nights if bath lights were turned off. Hot water pipes freezes before cold.

Need to have someone open the wall to find out why pipe is freezing. In the above situation pipe was run toward the outside of the stud, insulation between the pipe and the inside of the wall and no insulation between outside and pipe.

Plumbing should not be in exterior walls.

Open the cabinet door to let heat in. Leave lights on. If possible put a light with 60w blub in the cabinet. That will generate some heat. No need to call plumber unless pipe burst and you won't know that until it thaws.

I had a call last winter where pipe only froze on cold nights if bath lights were turned off. Hot water pipes freezes before cold.

Need to have someone open the wall to find out why pipe is freezing. In the above situation pipe was run toward the outside of the stud, insulation between the pipe and the inside of the wall and no insulation between outside and pipe.

Plumbing should not be in exterior walls.

Thank you so much for your quick response! Will try all your tips!

If the pipe is still frozen at this time AND is made of metal (copper or galvanized) I would recommend that you continue trying to thaw the hot water pipe using the hair dryer. Here, metal pipe can act as a conductor of heat and may conduct the heat far enough along the length of the pipe and into the wall to thaw that pipe. Keep the dryer about 1" off the pipe and it may take 15-20 minutes (so give the hair dryer a break every 5 minutes or so), but in a lot of cases this does the trick.

The single most important thing to know when thawing a pipe is to be sure that the hot tap is fully opened. In this manner, as the pipe starts to thaw you will see some dripping start to occur and that means that you are close and to just hang in tight... pipe will thaw quickly from there... ;)

As Hkstroud mentioned, if the pipe thaws and is burst it will be obvious as you will hear a firehose running behind the wall. In this case, you'll need to know where the main water shutoff is (or the cold water valve into the water heater) so you can shut the water off and call a plumber to make the repair!

In the future, keep the cabinet open on those extremely cold nights or, if absolutely necessary, leave the hot tap with a slight drip overnight... should keep this from happening again!

Mark

If the pipe is still frozen, I would turn off the water to the house anytime I left home. Just in case a warm front moved in.