One radiator stays cold

Jgilly771

I have an apartment that has one zone with 7 forced hot water radiators. Burnham boiler, new pump. 6 of the radiators both suppy and return lines get and stay hot. The 7th radiator does not get hot. This radiator is furthest from the boiler. Its the smallest in the apartment. The supply line gets cool about 10 feet from the radiator. The return is icold. I bled the radiator and the supply got hot. No air was found in the system. The return stayed cold. I purged the return line it stayed cold. I shut off valves for other 6 radiators no change. Removed radiator found some fine sediment (no chunks). Flushed it out and still nothing. Any thoughts on what to do?

neilc

so you control the boiler?
to remove and check that radiator you took pressure off the system ?
Do you have enough static pressure to reach back up to that rad with the circulator turned off ?

Jgilly771

Drained the system and removed that radiator. The radiator had a lot of water in it and I could get water out of the bleeder valve. I got all the sediment out of the radiator. Flushed it out 4 times until clean & clear water came out, reconnected and bled.

SuperTech

Can you get pictures of the piping? Perhaps this radiatior isn't piped in correctly. Of course you have to be sure you have proper flow to the radiatior and all the air removed.

Has it ever worked for you? You mentioned it was furthest from the boiler, is the closest one hottest and does each radiatior get cooler the further it is from the boiler?

neilc

how are your rads piped back to the boiler?
for this rad not to heat when the rest do, it, or all of them are piped back to a manifold ? Pex? copper? or iron ?
If that rad was full of gunk is the return blocked somewhere?
post a picture of the boiler, circ, and pipes going and coming

Jgilly771

SuperTech

What is the pressure in the boiler at its highest temperature?

From those pictures it doesn't look like anything has ever been modified from the original installation. It must have worked at one time. That would lead me to believe it's either an air or water flow issue

Jgilly771

First, thanks for the quick responses. This is a great forum and I appreciate the help on NYE.

Supertech: I bought the building two years ago. I talked to the previous owner tonight and he said sometimes it worked sometimes it didn't. He tried to get it to work but never could consistently.

neilc: My best guess is that the return is blocked. If this is the case is the only way to resolve replacing the pipes? I am meeting with a plumber at the property tomorrow morning.

Jgilly771

The pipe with the hose is the return, the pipe to the right of the one with the hose is the supply.

Also, all other radiators seem to get same temp.

Jgilly771

Water pressure is between 20-30 psi at highest temp

SuperTech

Is it possible that the radiatior isn't pitched/leveled correctly? I've seen that before where old floors settle and the radiatior is pitched away from the bleeder vent and an air pocket gets trapped. Perhaps flow isn't adequate due to low water pressure?

Jgilly771

Could be. but tonight I opened up the coin vent and bled out a couple gallons of water. No air came out. The water turned from cold to hot eventually. The return never warmed up. Leads me to guess its a water flow problem.

JUGHNE

A New Years Day plumber...that is something!

Could be pressure problem.
Is there a valve on the inlet, did that look like it was fully open?
Some old valves were spool type that had a very small opening when off to insure a small water flow. On some of these the knob/shaft while turning freely would disconnect from the spool.

I wonder if this was a gravity system originally and was split up for 2 boilers?

The boiler to the right in the picture looks to have a severe reduction in the vent flue pipe...or not?
I would ask him about that also.

Jgilly771

Hahaha..He's my brother in law...My regular plumber has been trying to get it to work but can't seem to fix it. So I had to call in a favor.

SuperTech

If you bleed air out of the vent and get water, stop. It's not an air problem. No need to drain a gallon, never mind several.

It's a flow problem. Can you get a picture of the pressure/temperature gauge on the boiler?

neilc

on that return,
are there any other valves between the hose and the boiler?
or,
if you open the hose now,
do you get hot water back from the return from the boiler?
or better yet,
if you leave it open long enough,
will hot go up to rad, and return to that hose?
shut the circ off and just let system pressure push the water around.
Your filler works well, right ?

SuperTech

Yes. If you purge the zone and the radiatior is completely bled of air you should have hot water at the radiatior when you have hot water coming out of your purge valve.

Jgilly771

I can get pictures of the pressure gauge in the morning when I will post.

On the return. If I put my hand on the pipe closer to the boiler from the hose the pipe is warm. It continues to be warm for about 2-3 feet of the pipe between the hose and the radiator. After the 2-3 feet the pipe is cold. So when I open up the valve the water is hot for a bit, due to the warm water as described

neilc

wondering if the circ is weak,
and not enough "push" to flow all your pipe runs there.
any control valve at the rad ?
I'm trying to isolate flow one direction or the other somewhere on that bad rad line.

JUGHNE

Also pictures of the cold rad, include the inlet and outlet connections.

Jgilly771

Jgilly771

How can I check to see if circulation is weak? The pump is a new Taco 007.

SuperTech

That's kinda hard to judge without proper tools. You can get an idea by how long it takes for hot water to get from the supply manifold back to the boiler.

Do all of the other radiatiors heat evenly and normally?

Jgilly771

Yes, all the other rads heat up evenly and normally. I have attached a pdf with a sketch of the apartment. Rad 7 in Bedroom #4 is the cold rad. This apartment is on the 2nd floor of a three family. The boiler is located approximately under Bedroom #2.

neilc

I wrote everything below, and then thought,
let's try easy first,

easy enough,
do you have control valves on the working rads also? yes? good.
do they turn? yes? good.
shut them half way and see if this doesn't force flow to the cold rad. try a little more than 1/2 way , , , throttle them.

OR,
harder,
all right, let's try this,
I'm gonna assume in your boiler picture the one on the right is yours, or that the one on the left is piped the same way with a ball valve and purge drain above the circ.
and I'm assuming there are control valves on your working rads, and that they turn.
let's shut the valves on the working rads, and make sure the one on the cold rad is open.
In the basement,
shut off the boiler, the service switch.
close the ball valve above the circ,
put your hose on the bib above the circ ball valve and let that flow.
This should drive boiler feed water all up thru the cold rad, and back down to your hose, the hose should run cool, cold, and then boiler temp hot.
You may force hidden air this way, and this is the intent, that and to prove flow thru that circuit.
Keep an eye on the boiler pressure, and use the fast fill to keep pressure up.
once you have hot water back to the hose, and the water is running air free, shut the bib off, open the ball valve at circ, open the good rads , turn on the boiler and let's see what you get.
At worst we go back to the working rads and throttle them closed a bit to force flow to the cold rad

JUGHNE

From looking at the rad pictures, am I seeing the inlet on the top and the return on the bottom on the same end?
If so, are all connected this way?