On Sep 16, 10:24*pm, Tom wrote:
We have hot water radiant heat in our house. *After having our bathroom re-tiled, the radiator now sits 3/8" higher than previously so the two pipes coming out of the floor are 3/8" too short. *I cannot remove the 3/4" steel pipes, because I do not have access to the other ends. *A male/female coupling extends the pipe too much (about an inch) and I do not want to put the radiator up on blocks.

How much pipe is sticking out of the floor? You say you
can't add a coupling because it would then be too long.
But if there is enough pipe to work with, you could cut off some of
the pipe, re-thread, then use the coupling, nipples,
etc to make it back up. That assumes you have enough
clearance from the wall for access.

Another option as someone else suggested might be to
get a different radiator.

If you're not familiar with plumbing like this, I'd call in
a pro. What you think is impossible they may be able
to do in a couple hours.