Anyone know why wiggling riser would cause radiator to heat?

Matt Valencius

There was a horizontal run of pipe under the radiator that was pitched the wrong way due to settling of the house (built in 1922). Raising the entire radiator on shims (thus raising the pipe) solved the problem.

Matt Valencius

Anyone know why wiggling a riser would cause radiator to heat?

I have a single pipe steam system (operating between 0.5 and 1.5 psig!).

Everything works fine except one problem radiator, up on the second floor.

It is served by a 1.25 inch (or so) riser and has been stone cold. It is shimmed up a bit so that it tilts towards the supply (I checked with a level!). The supply valve body gets very hot, but the radiator does not. There is no water hammer or anything, it just stays cold.

I tried replacing the radiator vent, and although I can hear a little puffing coming from it now, it did not solve the problem.

I then had a plumber take a look at the supply valve. The valve was fine and the radiator did not appear to be clogged (nothing came out of it and you could blow air from the vent tapping out the supply tapping).

We were stumped as to why the radiator was not hot (I thought for sure it was the supply valve!). However, when we put the radiator back on and re-started the heat -- the radiator mysteriously began heat up. Not super hot, but not cold either.

I am now wondering if wiggling the return somehow let the steam through. The only other time I have convinced this radiator to work was when I was putting shims under it to adjust the tilt. In the course of tilting the radator various ways, it all of a sudden started to heat up.

Does anyone have any idea what could be causing the problem? Clogged return? Aliens? : )