Radiator loud knocking and not heating

DPK99

Greetings. I have a single line steam system and all is good, but one radiator in the bathroom isn't heating up. The intake valve seems to get warm, but no part of the radiator itself heats up. In addition, I hear that loud knocking sound from this radiator when the boiler fires up, which tells me some steam is entering and hitting water, based on what I've read. The valve is in the full open position. I have tried a new vent, and even no vent, just incase air was not escaping. I have added a couple of shims to make sure that the radiator maintains a slight leann and checked with a level. Now, I'm not sure what to do? What's the next step? Thanks!

EBEBRATT-Ed

Check the piping that leads to the radiator (the run out) and make sure it's pitched correctly. It should be pitched upward in the direction of flow. Hopefully this is a first floor bathroom with the piping exposed in the basement

It's also possible the radiator valve has a broken disk inside or is not fully open

DPK99

Actually, this radiator DOES heat up, but takes longer than the others. So the issue is the knocking sound and slower heating.

ethicalpaul

My money would be on standing water in the supply line to that radiator, caused by improper pipe pitch probably caused or exacerbated by settling. I agree with @EBEBRATT-Ed who I've never seen giving bad advice!

MaxMercy

ethicalpaul said:

My money would be on standing water in the supply line to that radiator, caused by improper pipe pitch probably caused or exacerbated by settling.

If that's the case and the pipes are buried, is it possible to remove a vent at the radiator and blow the water back toward the boiler with a compressor? If the steam is dry, would this be a long term solution or something that would need to be done fairly often? If these questions are asinine, don't be afraid to tell me!! LOL.

ethicalpaul

Your questions are fine! But that solution won't work due to the nature of how steam heat works.

The steam condenses into liquid water in the radiator, and then the water has to have a downhill ride all the way to the "wet return"--the place where the return line meets the boiler water line.

If you were to blow out any standing water, it would just refill the next time steam started condensing in the radiator.

There is another recent thread on here where the homeowner was disconnecting a union in his return pipe in order to drain water from it periodically, but that's not a good solution.

It can be a real pain with these pipes that are between floors or in the wall. I had the same situation you describe so I ran a new supply pipe in my dining room to the bad radiator! See the saga here: https://forum.heatinghelp.com/discussion/167233/fixing-pitch-issues-in-old-house

MaxMercy

ethicalpaul said:

If you were to blow out any standing water, it would just refill the next time steam started condensing in the radiator.

Ah, understood. I was thinking that most of the condensation would take place in the heat exchanger (radiator), and maybe clearing the water might be a once or twice a year thing, but rereading the OP I see it's a one pipe system so my question was dumb.

Thanks for the explanation Paul! I've never seen a steam heat system, but they fascinate the beejeezus out of me, particularly since joining this forum.

EBEBRATT-Ed

@ethicalpaul

Thank you!. But I frequently give bad advise. Sometimes I type before I think.

How Is your new boiler running?

DPK99

Ok, some more info to provide. And thanks for the info so far.

I closed the radiator intake valve and when the boiler fired up, the knocking was still there. I though it was coming from inside the radiator, but now I realize it was coming from the pipe itself. Perhaps even louder than before when the valve was closed. This radiator is in the second floor bathroom, above the kitchen, and I noticed that it was extremely loud above the kitchen, to the point where I thought I heard some debri move in the ceiling above the kitchen. So I opened the valve back up and hopefully it won't knock as loudly.

Taking the advice given, I'm thinking there is standing water somewhere in the piping and when the steam contacts the wayee, it condenses rapidly and shoots into the pipe. I'm thinking that the water must eventually evaporate and then steam gets into the radiator and it heats. Does that sound plausible? 

If so, what are the ways I can diagnose the standing water location and try to fix?

ethicalpaul

Yes, @DPK99, what you describe sounds right to me. That's how my bedroom radiator was...after a long call for heat, the steam would heat the standing water until the standing water was right about at 212 (I surmise). Then it would quiet down and start to heat (because the water was no longer killing the steam. Or at least wasn't killing it as much, and wasn't causing any hammer.

It makes perfect sense that you are hearing hammer in the supply pipe. Most likely in a short horizontal section in the ceiling/floor just before it gets to the radiator (that may have developed a "valley"). And the sounds can sound like debris getting shaken around, but that is likely just the water getting shot against the pipes.

Can you try to slowly and carefully raise the radiator over several days to see if you can "unkink" the pipe? That's the easiest thing to try.

My boiler is doing great @EBEBRATT-Ed, it's getting downright boring!!

EBEBRATT-Ed

@DPK99
I agree with @ethicalpaul Get some scraps of wood and shim the radiator up. Use a crow bar and a block of wood for leverage. Use a level and make sure the valve end is slightly lower that the other end. Rais it a little at a time . Try 1/4" then go to 1/2" if you have to. Don't force it to much if it won't go up

DPK99

As a couple of you have suspected, the culprit seems to be an improperly pitched pipe section due to settling. The reason I know is because there was a steam leak above the kitchen, and it required cutting open the wall and repairing that section of pipe, which just happens to be near the improperly pitched section, which I used a level to determine. It was suggested to me that the hammering was probably what eventually damaged the pipe joint, which makes me shake my head that the previous home owners must have let it go for a very long time.

Unfortunately, these pipes are wrapped in asbestos, so that's an added expense, though not nearly as costly as I thought to have removed. 

I don't think I can pitch the pipe up any further from the side closer to the radiator, and that radiator is, of course, mortored into the bathroom floor, which makes it a challenge to raise.  So it will likely require lowering from the other end, where it makes a 90 degree turn down to the basement.

DPK99

Just realized that I placed this thread in the gas heating section, instead of steam. My bad. 

Erin Holohan Haskell

DPK99 said:

Just realized that I placed this thread in the gas heating section, instead of steam. My bad. 

@DPK99, I've moved it to Strictly Steam.