On Wed, 27 Jan 2016 22:45:30 -0500, dgk wrote:

I recently had the (electric) hot water heater replaced. Because of
code changes, the installer had to redo the power line (a 240 plug was
no longer allowed, it had to be straight through) and fix some pipe
size issues with the third pipe (not hot, not cold, but some emergency
feed).

It's a wide-spread Florida house, so all on one floor and the master
bathroom is on the opposite side of the house from the heater which is
in the garage. It takes about a minute to actually get hot water.

A few days after the heater was installed, I noticed that there was
some air in the hot water line in the shower, just about at the time
that the hot water finally arrives. It's really only noticable in the
morning, but it's getting worse, not better. I figured that maybe it
was air trapped in the system, but it's been about a month and I would
guess that the air should be out by now.

I tried the hot water in the bathroom located near the heater and it
happens there as well. So I suspect the hot water heater is somehow
letting air into the system. I have no idea how that could be since
water is sort of pressurized, but I don't know what else it can be.

The plumber says that it can't be from the hot water heater.

Can someone suggest how it could be the hot water heater, or what I
can do to find out how air is being introduced? Should I just try
bleeding the whole house by leaving all the faucets open for 10
minutes or so?

Put a pail under the relief valve pipe. Then lift the lever on that
valve to release the air. Leave it open for a minute or so, but dont let
the pail overflow. Dump the pail in a sink or outdoors and that should
solve the problem.

If you have a well, you could have a pump problem, well water is low, or
leaking pipes in the well. But then the cold water pipes would have air
too.