Steam radiator flushing

nieusna · March 17

Old 1-pipe steam system has been limping along with lots of drama: Hisses, gurgles, bang, clicks, etc. Radiators heat on inlet side only 1/3 or 1/2 way along the length. The system has not been maintained of flushed for a while. I assume it's all sludged up. Contractor bid to replace boiler, but would only fill and drain system with chemicals. I assume that won't be enough to open up the rads. Advice? I'd like to ensure the rads are properly clear before committing to the new boiler. Am I under estimating what a chemical fill and drain can do?

I'm new to the forum and did my best to see if this has been addressed, with no luck. I'm in Albany, NY area and would love to bring in a reliable pro to help get me sorted.

ethicalpaul · March 17

The radiators are almost certainly not the problem and are not sludged up.

Long Beach Ed · March 17

Your problem is not "sludged up" radiators. Nor do you likely need a "boiler replacement".

A "chemical fill and drain," whatever that is, will not correct your problems.

Find a qualified professional to evaluate your system.

Jamie Hall · March 17

The radiators on a one pipe steam system don't sludge up. There's no way for sludge to get there. However, there are two critical points. First, the inlet valve has to be open all the way. All the way, all the time. Second, and perhaps even more important, the vent on the opposite end has to be working — and they fail over time. In your situation, I'm going to bet on vents which have failed over time. This is not a hard fix — although getting the venting right, to get the system nicely balanced, is a bit tedious.

Gurgles and bangs are sometimes radiator inlet valves only partly open — or, much more likely, places where the pipes have lost their proper pitched. All the pipes from the radiators must be pitched so that water can easily drain back out of them to the steam main, and the steam main must be pitched so that water can get back to the boiler.

So the place to start for the gurgles and bangs is to go over every inch of all the pipes and make sure they still have the proper pitch. Use a level — don't estimate by eye.

nieusna · March 17

Thanks for the details, Jamie. Very helpful. I was about to write that all inlet valves were open, since I know that rule. But I thought I better check first. Indeed, half of them were half closed! I instructed tenants to leave them alone, but should have known better and checked. All vents were replaced some years ago, but I'll have those checked too. For pitch, the house is sagging here and there, but all pitches are at least 1"/10'. Some are more steeply pitched, because of the sag. Is 2" or 3"/10' too much. What problem would too much pitch create. I appreciate the input. And so quickly. Glad I found this forum.

AdmiralYoda · March 17

Radiator vents are a maintenance item and do fail. For whatever reason the vents in my one pipe system only last 3-5 years. What pressure is your boiler operating at? Too high of a pressure can prematurely damage radiator vents.

Jamie Hall · March 17

Too much pitch never hurt anyone — unless it means that something else has too little.

One not so obvious thing to check is to make sure the pitch on long runs is reasonably consistent. You wouldn't think so, but even a two inch pipe can sag in the middle.

nieusna · March 17

On quick inspection, pitch looks good everywhere except very bottom of run in photo, but I think that's below water line so should be okay, right? I'll check all lines more systematically in better light. To prior question, system is operating at 2 psi. I just ran one heat cycle with valves properly open: surprise, much better! A rookie mistake, I know, so I appreciate the guidance!

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bburd · March 17

Your boiler has a "colliding header", which can cause water to be thrown up into the steam piping along with the steam. That is likely part of your problem. Unfortunately correcting it would require re-piping the header, which would be very costly. This is something to keep in mind when the boiler needs to be replaced.

nieusna · March 17

Oh, good to know. No one has noticed/mentioned that. I'll take note and add it to my list for researching. Quick follow-up: Would this likely be corrected with a new boiler install, or would it entail more serious re-plumbing of the system?

bburd · March 17

When the boiler needs to be replaced, that would be the best time to pipe the header in accordance with the manufacturer's minimum requirements as shown in the boiler manual.

The boiler steam risers should enter the header before the steam main takeoffs, followed by the equalizer drop at the end. Proper pipe size is also important.

The main function of the header is to separate steam from boiler water to ensure that only dry steam rises into the steam mains.

Jamie Hall · March 17

The somewhat wonky piping around the boiler isn't helping — but it isn't going to hurt enough to be worth doing anything much about until you need a new boiler — which may be quite a while. Then it won't be that hard.

In the meantime, patience. But glad that getting the valves right helped!

Steam radiator flushing

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