Steam base radiator, sometimes hot and warm, other times totally cold, why?

georgearoush

My apartment is heated with steam based radiators. All eight radiators are single-pipe systems with air vents. Most of the time, all the radiators heat up just fine. However, occasionally, one or two radiators fail to heat up at all—and this can go on for 2–3 days, and then, out of the blues they start to heat up again!

What’s puzzling is that it’s not always the same radiators that stop working. If it were, I’d have a clear place to start troubleshooting. I’ve already replaced all the air vents and checked the valves, so those shouldn’t be the issue.

When a radiator doesn’t heat up for over a day or two, while the others are heated, the "fix" I’ve found is this:

1. Remove the air vent.
2. Place a vacuum hose over the vent opening.
3. Run the vacuum for 1–2 minutes until hot air starts flowing into the radiator.
4. Place the air vent back on.

After doing this, the radiator heats up normally when the boiler is running, at least until it cools off again.

Does anyone have an idea what might be causing this intermittent issue?

Big Ed_4

Seems like there is water trapping in your steam supply . Check the supply valve first..

ethicalpaul

I too would be looking for places where water could be collecting, but if the issue moves around to multiple radiators, that makes that possibility less likely (unless several radiators all have supply pipes with water trapped in them).

Another cause could be radical overventing of many radiators. In this case, the steam will just go "wherever" in unpredictable ways.

georgearoush

I continue to experience an issue with my single pipe steam based heating system. To summarize: some radiators heat up as expected, while others remain cold for 2-5 days at a time and then work just fine.

For over a week now, I’ve been tracing the pipe from a cold radiator back to the boiler in the basement. About 10 feet from the radiator, the pipe is completely cold. However, the section of pipe leading to the boiler is very hot — too hot to touch for more than 2-3 seconds. At first, this suggested a blockage at the transition point between hot and cold, but this "hot/cold boundary" is not fixed. Its location varies along the pipe, and I’ve observed this behavior with other radiators as well, and again, the "hot/cold boundary" is never at a fixed location on the pipes.

I’ve already tried disconnecting the valves and noticed no water coming out. I also ensured that the radiator is pitched correctly (downward toward the valve). A temporary fix I’ve found is to remove the vent (or valve) and use a vacuum to draw steam into the radiator. This gets the radiator working properly again, but the issue returns after 3-5 days (and will fix itself after 2-5 days).

If the problem were isolated to a single radiator or pipe, I would assume it’s a localized issue. However, the randomness of the affected radiators and the fact that the "hot/cold boundary" is never fixed on the pipes makes this puzzling.

Does anyone have any ideas about what might be causing this?

Jamie Hall

The system, for some reason, is trapping water in the runouts or mains which are affected. There could be any number of reasons for this…

But. Go back to square one. Is the near boiler piping decent? Doesn't have to be perfect, but is it arranged so that any carryover can't get into the mains? Then trace every inch of main and runout. The question you (and your handy level) are working on is how would any water — condensate — which got into the pipe at this location make its way back to the boiler?

What I think may be happening is that you will get pools — maybe outright lakes — of condensate in various locations in the piping due to inadequate pitch or pitch in the wrong direction (any drips to a wet return on the system? and those pools, which will move slightly depending on which radiators are working, are stopping the steam, or at least slowing it enough to be problematic.

Worth a try, anyway.