Blocked Hot Water Radiator Return Line

[Joe Jor]

Howdy gang!
I have a 100 year old house in NY.  After draining the hot water radiator system over the summer to replace a number of values, I was able to represurize the system without leaks.

Once the heat started being used this winter, the tenant reports that a single radiator that will not get hot; all the other radiators work perfectly.  I called a plumber out.  He diagnosed that the return pipe is blocked.  His suggestion was to rip out the plaster walls to trace the pipe to either replace the piping or determine the location of the blockage so it can be addressed.

This sounds very drastic and expensive to me.  Has anyone heard of another way to jar a blockage loose?  The pipe is a 3/4 inch; there are no drains on individual radiator runs in the basement ... only a master drain for the boiler.

Joe