Blocked Hot Water Radiator Return Line

[Joe Jor]

Howdy gang!
I have a 100 year old house in NY.  After draining the hot water radiator system over the summer to replace a number of values, I was able to represurize the system without leaks.

Once the heat started being used this winter, the tenant reports that a single radiator that will not get hot; all the other radiators work perfectly.  I called a plumber out.  He diagnosed that the return pipe is blocked.  His suggestion was to rip out the plaster walls to trace the pipe to either replace the piping or determine the location of the blockage so it can be addressed.

This sounds very drastic and expensive to me.  Has anyone heard of another way to jar a blockage loose?  The pipe is a 3/4 inch; there are no drains on individual radiator runs in the basement ... only a master drain for the boiler.

Joe

[Jim K.]

@Joe Jor

My first reaction reading this...what??? This is a 100-year-old house. You say you've changed "a number of values." Do you mean valves? Which valves? How did you drain the system? How did you fill the system again? Did you do this work personally or did someone else do it for you?

The next thing I've got to ask if it's a monoflow or older, modified gravity-fed system. Please watch this video. BP moderators and content checkers, please don't delete this as self-promotion, it isn't. I have no affiliation with This Old House and they're not going to mind my posting a link to their video here -- this is public television.

How to Diagnose Problems with a Hot Water Heating System | Ask This Old House

[Joe Jor]

@Jim K.  Sorry about the typo, I meant **valves.**  The 90 degree right angle radiator valves were swapped out on many other radiators; this one was not modified.  The valve on the cold radiator were replaced in 2014 when the valve started leaking; it had been working since.

It is a monoflow system as it is similar to the one shown in the video at 3:30 - 5:00.

Joe

[Joe Jor]

Couple more details, I missed.  I had plumber replace the values in 2014.  I did many of them over the summer.  The whole HW radiator system has a single hosebib; A hose was hooked up to drain into the main sewer access.  To fill, we just turned the HW system water feed on again and got it up to pressure.

Joe

[Jim K.]

@Joe Jor

OK, monoflow system, life just got a lot easier. Did you bleed/burp this radiator when you filled the system? I know it's a basic question, but we both know that valve hasn't gone bad since 2014.

[Joe Jor]

When I filled the system, all radiators on all floors were bled, including the cold one.  They were bled again while the plumber was on site.  Additionally, the plumber who stopped by disconnected the radiator and tested both valves (it has one on both the fill and return sides) to ensure they worked.  This was the process that he determined that the return line was blocked: fill side feed pipe got hot (while bleeding), return side never got warm.  While the radiator was fully disconnected, he shined a light through the rad end-to-end to make sure there was no blockage.

One more detail: this is a 3 story house, cold rad is on the 3rd floor.  The other 4 rads on the 3rd floor are hot.

Joe

[Jim K.]

@Joe Jor

Thanks, Joe. Here's what I would try for this: drain the radiators on the third floor. Buy a basic 25-foot 1/4 in. drum plumbing auger for drains, here's a link to one:

Basic drain auger

Disconnect the radiator on the return side. Cut the thicker augering element off the auger with a hacksaw or a disc on a rotary tool, use pliers to stretch out the next three or four spirals of the auger spring line. Feed the 1/4 in. auger line into the return line. You should be able to feel if there's a blockage and if there is, you should be able to auger through it with the auger modified as I've described.

You've done a lot of work on this system, replacing all the valves. You clearly understand how this thing works. If the solution I've described doesn't get you anywhere, yes, the next step is busting out of the line and replacing it, but let's cross our fingers.

[Joe Jor]

@Jim K.  I asked the plumber if there was some kind of snake that existed for the radiator pipes.  He looked at me like I was crazy!  I guess you and I were both thinking the same thing.  Thanks for the suggestion, I will give it a try.

I had never see this possible solution before.  I wonder if it would work.  I also don't know where it is being done as I have never seen a radiator pipe that skinny in NY.

Joe

[Jim K.]

Originally posted by @Joe Jor:

@Jim K.  I asked the plumber if there was some kind of snake that existed for the radiator pipes.  He looked at me like I was crazy!  I guess you and I were both thinking the same thing.  Thanks for the suggestion, I will give it a try.

I had never see this possible solution before.  I wonder if it would work.  I also don't know where it is being done as I have never seen a radiator pipe that skinny in NY.

Joe

Huh. I might try that with an air compressor, not a bicycle pump.

[Erik B.]

My first thought when reading this was to remove the blockage w a snake so you guys are on the right track.

Second thought was to call a 2nd plumber before you start tearing apart the house. Would suck to open walls all over the place to only find out that is not the issue.

There are many tradesman out there who dont know what they are doing. If you dont clear it up in your own call someone else

[Judy Parker]

"One more detail: this is a 3 story house, cold rad is on the 3rd floor. The other 4 rads on the 3rd floor are hot...."

Is the cold radiator, on the 3rd floor, located the farthest away from the boiler? If so, crank the thermost up really high, and see if it finally heats up.

[Joe Jor]

@Judy Parker, Yup cranking the heat is a classic, I tried that one as well as pumping they system's PSI up to 27 lbs.  Unfortunately neither worked. :-/

Thanks for the ideas!

Joe

[Don Meinke]

We don't have that type heat here.MOST of those systems were taken out 30 to 40 years ago

Unless there is a reason not to, I would Try a blast of air, from an air compressor.  Limit the pressuré to whatever you consider safe.

Much like a cheetah tire bead seater.  They really make a shock wave that moves most anything.

[Don Meinke]

[George W.]

I highly doubt your return lines on a hot water boiler are clogged. First things first you need to lower your pressure on the boiler. The relief valve will start going off at 30psi. And if your expansion tank is under sized it will start going off. Pressure is unrelated to the amount of heat in water. The reason you need pressure is to move the water higher. 18psi of pressure is more than sufficient to reach a 3rd story of a house.

Did you check the 3rd floor radiators for air? Does your boiler have a spiro vent/ air eliminator? Is your circulator pump on the feed or return side of your boiler? How old is the boiler? Ideally the circulator should be on the supply side of boiler pumping away from the boiler and expansion tank for optimized performance. 

Hot water boilers are closed loop systems and once all of the oxygen that's in the water that initially fills it theres no reason for it to ever rust because that oxygen gets used up on a small amount of rust and it can't keep rusting because the oxygen is already "spent". The water acutally turns into ionized water and will no longer continuing corroding the system. Thus your return lines should never clog. Steam boilers are a whole different story. What color was the water? Black or red? If its blackish, then its ionized water and your in good shape. If its red then you have leaks in the system and fresh water is constantly being introduced and your pipes are rotting. If you acutally have clogged hot water pipes your water would look like red mud. 

My opinion as a plumber; youre probably not moving enough water GPM and feet of head. 

Did anyone change any piping? If so did they put in pex? Heating pex is highly restrictive per foot for flow compared to copper or black iron. 

Did someone replace the circulator pump? If so did they put in a taco 007? If so, and it's a monoflow system with a weighted check valve and many monoflow tees; you'd need a pump with a better pump curve in order to overcome all of that resistance in the monoflow tees and weighted chevkvalve. Taco 007's are not a one sized fit all. In fact most monoflow systems I see have the completely wrong sized pump on it and when I put the right sized pump on the "problem radiators" go away. Hot water boilers are all about moving water to convey BTUs from the boiler to radiators. 

Most old hot water systems are butchered by HVAC guys who primarily do forced air and diy's who don't know what they're doing at all. Don't butcher it further by opening walls and messing around with the pipes if you don't know what you're doing, you're asking for more problems. 

My advice: look at the circulator pump. It's probably not sized correctly for a monoflow system. My other second word of advice is to drop the other plumber who said its clogged and find a plumber who specializes in boiler hot water systems. 

[Ben F.]

could be a zone valve not working

[Sean McKenna]

@Joe Jor

Being air bound is the number 1 issue with water systems.

The first thing I think of is that you are in the wrong forums. Go to hvac-talk.com they have a section for home owners asking for advice. Try and be as clear as possible. Tell them what you have moving the water & pump size. What air separation method are you using.

Don’t go messing with the psi in the system. 1 psi will raise water 2.3 feet. You normally run those systems at 15-18 psi.

Blocked pipe!!!?!?!? NOPE. Doesn’t sound right. Steam systems can get blocked but water systems is not normal.

It is possible that when the valves were replaced one might be leaking air into the system. Or you might need another bleeder valve installed near that rad.

[Joe Jor]

Thanks for all the feedback!  It looks like the line burped and we again have heat in that cold rad.  I will have to prepare myself for a move invasive repair when/if I ever need have to drain the system again.

Joe

[Pat L.]

Originally posted by @Sean McKenna:

@Joe Jor

Being air bound is the number 1 issue with water systems.

The first thing I think of is that you are in the wrong forums. Go to hvac-talk.com they have a section for home owners asking for advice. Try and be as clear as possible. Tell them what you have moving the water & pump size. What air separation method are you using.

Don’t go messing with the psi in the system. 1 psi will raise water 2.3 feet. You normally run those systems at 15-18 psi.

Blocked pipe!!!?!?!? NOPE. Doesn’t sound right. Steam systems can get blocked but water systems is not normal.

It is possible that when the valves were replaced one might be leaking air into the system. Or you might need another bleeder valve installed near that rad.

Agree with this analysis. Air locks in our hydronic boiler system are the bane of these types of heating monsters. I periodically replace the corroded bleeder valves to correct this. BUT let the water cool down & drain that line to relieve the pressure otherwise you'll get covered in hot water.

[Account Closed]

Great thread. After reading others, and then the post from George W, this is a great example of how some things are ok for a DIY and some things are best left to a professional.

I've got a HW system in one of my buildings and have been looking into how it all works. I had/have no idea!!!

[Account Closed]

Originally posted by @George W.:

I highly doubt your return lines on a hot water boiler are clogged. First things first you need to lower your pressure on the boiler. The relief valve will start going off at 30psi. And if your expansion tank is under sized it will start going off. Pressure is unrelated to the amount of heat in water. The reason you need pressure is to move the water higher. 18psi of pressure is more than sufficient to reach a 3rd story of a house.

Did you check the 3rd floor radiators for air? Does your boiler have a spiro vent/ air eliminator? Is your circulator pump on the feed or return side of your boiler? How old is the boiler? Ideally the circulator should be on the supply side of boiler pumping away from the boiler and expansion tank for optimized performance. 

Hot water boilers are closed loop systems and once all of the oxygen that's in the water that initially fills it theres no reason for it to ever rust because that oxygen gets used up on a small amount of rust and it can't keep rusting because the oxygen is already "spent". The water acutally turns into ionized water and will no longer continuing corroding the system. Thus your return lines should never clog. Steam boilers are a whole different story. What color was the water? Black or red? If its blackish, then its ionized water and your in good shape. If its red then you have leaks in the system and fresh water is constantly being introduced and your pipes are rotting. If you acutally have clogged hot water pipes your water would look like red mud. 

My opinion as a plumber; youre probably not moving enough water GPM and feet of head. 

Did anyone change any piping? If so did they put in pex? Heating pex is highly restrictive per foot for flow compared to copper or black iron. 

Did someone replace the circulator pump? If so did they put in a taco 007? If so, and it's a monoflow system with a weighted check valve and many monoflow tees; you'd need a pump with a better pump curve in order to overcome all of that resistance in the monoflow tees and weighted chevkvalve. Taco 007's are not a one sized fit all. In fact most monoflow systems I see have the completely wrong sized pump on it and when I put the right sized pump on the "problem radiators" go away. Hot water boilers are all about moving water to convey BTUs from the boiler to radiators. 

Most old hot water systems are butchered by HVAC guys who primarily do forced air and diy's who don't know what they're doing at all. Don't butcher it further by opening walls and messing around with the pipes if you don't know what you're doing, you're asking for more problems. 

My advice: look at the circulator pump. It's probably not sized correctly for a monoflow system. My other second word of advice is to drop the other plumber who said its clogged and find a plumber who specializes in boiler hot water systems. 

 Ok! Can I steal the thread a bit?

I have a hot water system that actually works too well!!! It is super touchy and goes from needing a degree or two more to crazy hot. While that is one issue, the other issue is the system is about 100 years old, and I don't know how to take it apart so I can paint/re-drywall behind the units. I looked at a few videos and was warned that because the system is so old, the chances of getting it apart and back together are slim, and it's probably best to leave it alone. Also in the same vein/problem, I have a radiator in the bathroom that I would like to get behind, but was thinking of maybe just removing the entire thing - can I do that? Of course the pipes are in the walls and floors and possibly connected to other units (2nd floor duplex unit), but I was sort of thinking I could remove the radiator and replace it with a connector pipe, essentially converting the unit from a full radiator to just one warm pipe - I dunno...The whole thing is perplexing and I wanted to get as much info as possible before I do anything myself or even call a plumber to mess with it. Thoughts/Advice???

[George W.]

Originally posted by @Account Closed:

Originally posted by @George W.:

I highly doubt your return lines on a hot water boiler are clogged. First things first you need to lower your pressure on the boiler. The relief valve will start going off at 30psi. And if your expansion tank is under sized it will start going off. Pressure is unrelated to the amount of heat in water. The reason you need pressure is to move the water higher. 18psi of pressure is more than sufficient to reach a 3rd story of a house.

Did you check the 3rd floor radiators for air? Does your boiler have a spiro vent/ air eliminator? Is your circulator pump on the feed or return side of your boiler? How old is the boiler? Ideally the circulator should be on the supply side of boiler pumping away from the boiler and expansion tank for optimized performance. 

Hot water boilers are closed loop systems and once all of the oxygen that's in the water that initially fills it theres no reason for it to ever rust because that oxygen gets used up on a small amount of rust and it can't keep rusting because the oxygen is already "spent". The water acutally turns into ionized water and will no longer continuing corroding the system. Thus your return lines should never clog. Steam boilers are a whole different story. What color was the water? Black or red? If its blackish, then its ionized water and your in good shape. If its red then you have leaks in the system and fresh water is constantly being introduced and your pipes are rotting. If you acutally have clogged hot water pipes your water would look like red mud. 

My opinion as a plumber; youre probably not moving enough water GPM and feet of head. 

Did anyone change any piping? If so did they put in pex? Heating pex is highly restrictive per foot for flow compared to copper or black iron. 

Did someone replace the circulator pump? If so did they put in a taco 007? If so, and it's a monoflow system with a weighted check valve and many monoflow tees; you'd need a pump with a better pump curve in order to overcome all of that resistance in the monoflow tees and weighted chevkvalve. Taco 007's are not a one sized fit all. In fact most monoflow systems I see have the completely wrong sized pump on it and when I put the right sized pump on the "problem radiators" go away. Hot water boilers are all about moving water to convey BTUs from the boiler to radiators. 

Most old hot water systems are butchered by HVAC guys who primarily do forced air and diy's who don't know what they're doing at all. Don't butcher it further by opening walls and messing around with the pipes if you don't know what you're doing, you're asking for more problems. 

My advice: look at the circulator pump. It's probably not sized correctly for a monoflow system. My other second word of advice is to drop the other plumber who said its clogged and find a plumber who specializes in boiler hot water systems. 

 Ok! Can I steal the thread a bit?

I have a hot water system that actually works too well!!! It is super touchy and goes from needing a degree or two more to crazy hot. While that is one issue, the other issue is the system is about 100 years old, and I don't know how to take it apart so I can paint/re-drywall behind the units. I looked at a few videos and was warned that because the system is so old, the chances of getting it apart and back together are slim, and it's probably best to leave it alone. Also in the same vein/problem, I have a radiator in the bathroom that I would like to get behind, but was thinking of maybe just removing the entire thing - can I do that? Of course the pipes are in the walls and floors and possibly connected to other units (2nd floor duplex unit), but I was sort of thinking I could remove the radiator and replace it with a connector pipe, essentially converting the unit from a full radiator to just one warm pipe - I dunno...The whole thing is perplexing and I wanted to get as much info as possible before I do anything myself or even call a plumber to mess with it. Thoughts/Advice???

Try lowering the water temperature on boiler 10 degrees. Probably has over sized radiators if its touch freely then too hot. You can remove the whole radiator depending on what type it is pretty easily. Sometimes the old raidiator valves have unions built in to come apart easier.