hammer noise - radiator grade or other causes?

mattm

I live in a 1910 era three unit row house near Boston. We have 11 radiators on our floor (the top floor). There are about 9 radiators on the second floor. The bottom floor removed all their radiators and have HVAC installed during a remodel.

The radiators are generally quiet. However, the one radiator that does make noise is in our bedroom (and thus wakes us up in the middle of the night). Last year, there was a constant rattling noise which was diagnosed on this forum (amazingly from an audio clip!) of a broken valve. We fixed the valve and the rattling stopped.

My memory of last winter was that after installing new vents on the radiators, and making sure they all drained properly that they were quite quiet. This year however, I've noticed a hammering noise in the radiator in my bedroom. The hammering is three to five loud clangs when the system comes on.

This radiator definitely drains correctly, and I believe the radiator on the floor below also drains properly ( I think). My question after this long explanation is: beyond a steam hammer, what could be causing this noise?

The only thing I can think of is that the radiator water appears much dirtier with a rusty-colored mud in the sight-glass. Any suggestions what steps I can take to eliminate this hammering?

Fred

A horizontal pipe that feeds that radiator (under the floor) may have lost its pitch. Try raising the entire radiator up, maybe a half inch and then re-pitch the radiator. That will give the pipe under the floor some pitch also.

mattm

Thanks for the comment. I tried raising the radiator and that seems to have made the noise worse, perhaps the pipe is hitting something under the floor now? The pipes are the least accessible since they are between two apartments, so I would like to eliminate any other potential problem.

Would dirty water be causing banging as well? I've taken a picture of the sight glass.

Fred

Is it water hammer or does it sound like expansion noises where the pipe may be rubbing/dragging against a joist or the floor? Also, where is the water in that sight glass? It looks like that boiler hasn't been services in a long time. Do you ever blow the LWCO down like you should? Time to have someone service that system.

mattm

Thanks for the response - I believe that I have the water hammer when it turns on, and that after trying to raise the whole thing I have some sort of fainter noise which could be related to the pipe rubbing or dragging against a floor joist.

The water level is about 1 inch below the level of the rust. The system was actually serviced last winter, as hard as that is to believe! If I manage to have it serviced again, what should I make sure that they do to the boiler?

I flush the LWCO (shown in the left of the picture), once a week, and more often during heating season. Every time I flush it the water it brown.

Fred

Tea colored water is OK. When they service the unit, there are a number of things that must be done and they may vary depending on the type of fuel (nat. gas, oil, other). One thing they need to do is clean that glass! All of the safty and operating controls should be tested. The water in that boiler should be 1/2 to 2/3's up the glass, when the boiler is idle.
Are you sure the supply valve for that radiator is fully open? If this is a one pipe system, the valve must be fully open. Even if you think it is open, the disc inside the valve could have come loose and may prevent water from draining out of the radiator.

mattm

Thanks Fred. This is a Natural gas unit. Amazingly, there was no glass here before and this glass was only installed last year - in no time at all it became filled with that junk. This photo was taken with the boiler running, which may account for the slightly lower level.

As for the valve to the radiator, I am positive that it is fully opened. A plumber replaced it last year. I would hope that after only a year the disc hasn't come loose!

As a general question about these radiator valves, can I leave it closed if I don't need the heat, or will the force of the steam on the closed valve break/damage the disk. You were the one to actually correctly diagnose, from audio alone, a broken disc on my neighbors radiator (the floor below) which was fixed and silenced a lot of the problem.

Fred

If you don't need heat from that radiator, turn the Vent upside down. That will prevent air from escaping and block steam from getting in. Shutting the valve may or may not work, depending on the condition of the valve but even new ones can let steam leak into the radiator and water can't get out.
If there is any way we can hear the noise from that radiator, it may help us diagnose the issue.

mattm

That's a good idea. I have a shut-off ball valve attached to the vent (although it is open in this picture), so steam should be blocked from getting in. It still gets pretty warm.

I tried to raise it up as you suggested but it didn't seem to make much difference, I'm going to try and bring it up a little more. In the attached link, you can hear the clanging - the last 3 out of 6 clangs. Picture of the radiator below.
https://youtu.be/20PHNdFFJHg

Fred

You have enough pitch on that radiator. I'm thinking the system pressure is the issue. It almost sounds like a little water boiling somewhere, maybe at the bottom of the riser that feeds that radiator. Water that maybe can't get back to the Main. I'd ask the building manager to check the pressure and to also check the pitch on the horizontal section of pipe that runs out to the riser that feeds that radiator. It may have lost its pitch or have a sag in it, holding some water. My first though, with that clanging at the radiator is a pressure issue.

mattm

Interesting, thank you. Just as an addendum - the radiator sits in a corner of the room has sunk over its 115 year history. As much as possible I have tried to raise the pipe, along with the radiator.

What should the system pressure be? Presumably, this means the pressure is too high? I should add that the riser this radiator is attached to is the shortest distance to the boiler compared with other (more quiet radiators).

I will check the horizontal pipe that feeds the riser when I get home (three unit building, so just neighbors, no manager)!

Jamie Hall

mattm said:

...the radiator sits in a corner of the room has sunk over its 115 year history. ...

Right. Check that horizontal runout, and, while you are at it, check the pitch of all the other more or less horizontal pipes in that area. You'd be surprised how little of a sag it takes to bang. And a horizontal more or less pipe has to have a real definite pitch to it -- just horizontal won't do it.

mattm

The pressure cut-in is set to 0.5 psi and the differential is set to 1 psi (for a total of 1.5 psi). So the pressure seems to be fine unless I'm missing something (could the pigtail be clogged?)

The risers are in a neighbors portion of the building, and are thus (temporarily) unaccessible. The horizontal run-out is similarly unaccessible as it is between my floor and my other neighbors ceiling.

A portion of the header that runs through a circuitous path from the boiler is definitely not pitched towards the boiler. Is that correct for the header? This is before it splits off into risers. There is great pitch on the returns that feed into the back of the boiler.

Returns at the back are pitched correctly (this is a one pipe system, but I can't see what they are draining.



Pressuretrol setting of 1 diff. 0.5 cut-in.



Black horizontal pipe in the foreground connects directly to the boiler without splitting. It is pitched away from the boiler.

Jamie Hall

There is no problem with a pipe pitched away from the boiler -- provided there is a drop to a wet return at the low end of it.

Fred

Also, I would say from the looks of that Pressuretrol, while it is set correctly, it hasn't been off of that pigtail in years. The pigtail is likely clogged and the Pressuretrol can't control the pressure.

nicholas bonham-carter

The addition of a low pressure gauge would show you what the pressure really was, instead of simply relying on the setting of a device we all distrust!—NBC

mattm

I believe Fred - the pigtail looks like it is hasn't been changed in years. If it is not controlling the pressure, would this lead to the furnace heating more, and for longer, than if it was at the correct pressure, thereby consuming more gas?