Single Radiator not heating & banging loudly

Prometheus

Hi,
New home owner getting used to steam heating. I live in a 2 story, 1800 sq-ft bungalow with a basement. Initially, when we first turned on the heat this year, it seemed like every radiator was clanging. After replacing a couple vents, repacking a few valves, and shimming up a few radiators, we've managed to mostly silence all the radiators save one. The radiator in our bedroom (probably the furthest from the furnace) has almost continual water hammer and is extremely slow to heat. When it does, it usually only heats the first couple fins and only on really cold days does it finally heat all the way across. When it heats all the way across, then it seems to quiet down a little, but it still occasionally clanks.

I'm wondering what I should do to troubleshoot. I was considering insulating some more pipes in the basement--I noticed most of the pipes are already insulated, but once the pipes branch towards this particular radiator, they abruptly stopped insulating, leaving about 8 feet in the basement and 8 feet on the first floor uninsulated. Is adding more insulation the right approach, or are there other more likely issues I should troubleshoot first?

Thanks,
Daniel

Jamie Hall

The second thing to do is going to be to insulate that 16 feet of pipe. That is almost sure to give you real trouble. But, before you do, check the slope of those runouts -- and not just end to end. Make sure there are no sags. You wouldn't think that a nice big pipe could sag, but they do. Get that nicely straightened out. Then insulate the pipes.

Then check the other usual suspects -- radiator tilted just a bit towards the inlet, and valve fully open.

ChrisJ

I doubt it's because of the insulation, but once this problem is fixed you should insulate the piping.

Do you know what specifically is hammering? The horizontal section of pipe, or the radiator? One of them is likely pitched wrong and holding water. Put a bubble level on them and check. My personal experience has been it doesn't matter a huge amount on radiators, but the pipes need to drain well.

If the pipe is almost level, or pitched the wrong way and holding water that's your problem.

Fred

Also make sure your pressuretrol is working properly and that the pressure is set to .5 PSI cut-in and a Differential of "1". That will cut the burner off at about 1.5 PSI. High pressures can also prevent water from returning to the boiler and can cause some water hammer. Make sure the pigtail (looped pipe that the Pressuretrol is mounted on) is clean as well. They can get clogged.

Prometheus

I'll definitely check the pitch when I get home, though it all looked right from a visual inspection last night. The radiator itself is pitched, I repacked the valve and made sure it was fully open and replaced the vent, so it shouldn't be any of those.

On the subject of insulation, are there any pipes that shouldn't be insulated? I noticed a couple other pipes that aren't insulated, including the 3" pipe coming straight up from the boiler, so I figured I would just go ahead and insulate all of them. I'm a little hesitant to insulate the pipes on the first floor, since they are fully exposed and insulating them would look ugly, so I was planning on not insulating those unless it's still noisy.

Jamie Hall

There usually isn't any real need to insulate pipes like the ones on the first floor. But as much as you can elsewhere...

Fred

That pipe on the first floor is providing some radiation/heat in that conditioned space and insulating it might affect the comfort level, of that room. If, by chance that room is too warm, insulation might help that a bit.

Prometheus

You guys have been great!
The pressure stroll was set to 2, so I turned this down to .5. I assume people turn this up in a misguided attempt to compensate for leaky radiators? I fixed a number of leaks, so that would make sense.
The pipes seem correctly pitched (though some of the quieter pipes seem about level, so that's a mystery.)
Insulation comes tomorrow.
The pipes are quiet now, but we'll see how they are at 4am, when they usually seem to decide it's hammer time.

nicholas bonham-carter

Is 4 am the end of temperature setback? If so I would eliminate the setback, and choose a constant temperature, 2 degrees lower as a constant setting. There are no savings in anything other than a setback longer than 24 hours.
Imagine someone driving on a log trip, constantly slowing down, then speeding up. A constant speed, and a (lower) constant temperature will be the most economical, as well as most comfortable.--NBC

Prometheus

The setback is more of a comfort thing than a savings thing--we like to sleep at 68 and wake at 72. I don't think our setback is quite that extreme. Is it bad do this, or merely not-energy-saving?

nicholas bonham-carter

Try a constant 69, and see if that keeps it quiet.--NBC