Only Hot Water Backs Up in Bathroom Sink

A “Car Talk”-like poser for plumbing:

Cold water drains just fine in our bathroom sink. Hot water, however, drains normally for a bit but then soon starts backing up. A plunger opens the flow right up again (no physical blockage apparent), usually with no more problem at that time. But whenever I’m back at the sink using hot water again, the same thing happens.

My wife theorizes that it may have something to do with air in the hot water, which does appear more aerated than the cold water — that the air somehow creates some sort of pocket or bubble in the pipe. 

I’ve searched for an explanation online and have come across a few mentions of the same odd phenomenon, but no real diagnoses. Any ideas out there?

is this new? If so how new?  

My, Ive stayed at Holiday Inn so can play a plumber idea is, that either there is much more volume of hot water for whatever reason or the hot water activates the residue of soap, lotions, etc in the bathroom pipes and therefore things slow down.

(fWIW years ago I switched to liquid soap from bar soap in the kids showers because they clogged so often, the switch fixed things)

Regardless, I’d call a plumber and have it snaked before it becomes worse. 

The hot water does drain, just very slowly, and the cold water is fine, so I don’t think there’s a blockage. Only liquid soap and shaving cream have gone down those pipes since a remodel five years ago. No noticeable difference in the volume coming from the faucet; if anything, because of the apparent aeration, the hot water may be less voluminous.

I began noticing the hot water issue about a year ago, I think, but since it’s more a mystery than a big problem, I haven’t kept close track.

Does Drano drain?

I agree with peteglider that the hot water could be softening up (and therefore expanding) any residue of shaving cream/hair/soap that is in the pipes. Cold water could be passing through the pipe because the clog is compressed and not affected by the cold water, but when the clog expands from hot water passing over it, the hot water cannot get through the narrowed opening in the pipe.

 We recently had to have one of our sinks snaked out and I told the plumber that we were careful about what went down that drain. He said that little hairs from shaving, from trimming one's bangs, or even just from combing your hair over the sink all combine in the pipes to make a clog that will eventually cause problems with the water draining.

I recently had a clog in my bathroom basin cleared by a drain cleaning firm.  The clog was several feet down the drain pipe and required two gallons of water to produce the backup in the basin.  Knowing that hot water takes some running to get to the tap, you may be experiencing the same kind of problem.  Try waiting until the drain pipe is dry for many hours (as long as you can) and then run cold water to see if there is a clog farther down.  It may not be a condition of hot water causing the backup.

This is one of the better DIY discussions in recent memory. All good ideas.

Thanks, everyone, for the good ideas and suggestions. I’ll start with mrmaplewood’s cold water test in the morning and go from there.