Uneven heating AFTER pipes insulated

Ray Reiter

One pipe comes out of the radiator, goes under the floor, and, in the crawlspace, connects to the main.

How do I unblock it? Wrap in heating tape, assuming that the condensate froze? (CAN the condensate freeze and block a pipe? I Googled "frozen steam pipe" and came up with exactly one hit, in Iceland, so this seems unlikely.)

Ray Reiter

Uneven heating AFTER pipes insulated

I have a one-pipe steam system, originally (back in the 30s) was built for coal. The pressuretrol is bottomed out (probably unchanged for years).

After insulating the (steel) steam pipes in a crawlspace under the house with fibreglass, the radiator on the second floor works fine, but of the two radiators on the first floor, one is cold, and the other (a baseboard) is near cold. (The pipes for all three of these radiators come of the same main pipe.)

But BEFORE I insulated the pipes, all the radiators worked fine, although with water hammer. I didn't hang on the pipes when I put the insulation on, I swear!

Other random facts about the system:

1. It looks like there are (new, shiny) vents on the main pipes down in the basement. But I do get hissing from the radiator vents.

2. At the start of winter, the water hammer was bad, and I went through and checked all the radiators for pitch (and added enough to make the level bubble move, about 1/8, to two of the radiators involved. The second floor one, which is hot, and the first floor one, which is cold.

3. All this happened during and immediately after a cold snap. Since the first floor radiator that is now cold is in an unused part of the house, I turned it off to end the waterhammer and get some slip. When I turned it on again, before insulating the pipes, I heard a trickle of condensate. Is it possible that somehow I've frozen the pipe?


I understand that steam heating is a system, not a collection of pipes, so probably I haven't given enough detail. But any hints would be appreciated.

Steamhead (in transit)

Are the problem radiators

at the end of the main? If so, you could have a blocked return from that main, whoch wold allow water to back up in the main. This could block the takeoffs to those rads and cause banging.

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Ray Reiter

I think they are at the end of the main

Thanks for responding

The order they come off the main is, starting from closest to the boiler:

1. First floor baseboard - partial to no heat

2. Second floor column to radiator (?) - good heat heat

3. First floor radiator - cold

There's no water hammer now, though. They are just cold.

What is a "blocked return"? It's a one pipe system...

Steamhead (in transit)

At the end of the steam main

a pipe will drop to near floor level or thereabouts and return to the boiler. It carries the water of condensation back to be re-boiled. If this pipe is blocked, water will back up into the steam main.

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Steamhead (in transit)

Where does the main go

after your radiator connects to it?

How is the water that accumulates in the main, returned to the boiler?

Take pics and post them here if you're not sure.

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