Several radiators not heating

sovavto

Need help after determining that my plumber didn't know what he was doing.

This is a gravity fed hot water heating system. Boiler in the basement and original cast iron radiators on 1st, 2nd, and 3rd floor. All original ones are working OK.



During a renovation project (when everything was open down to studs), 1 old radiator on 2nd floor was replaced with a new radiator (and it works OK), 2 new radiators were added where they didn't exist before (one on the 2nd floor, 1 on the 3rd floor). These 2 new radiators are not heating up.



When I open the vent valve on these 2 radiators, cold water comes out of them, so it does not seem to be air related.



In the basement, the 2 new radiators are connected with 3/4" pex. 2 supply pex pipes are connected to original metal supply and 2 return pex pipes are connected to original metal return. When examining the new connections in the basement, I can feel that the 2 pex supply pipes are warm for about the first 3-4 feet from where they are connected to the original metal supply, after that they become cold to touch.



Please let me know what could be causing the 2 newly added radiators to not be working and what might be done to get them working. If any further information is needed, I'll gladly provide it.

Alan (California Radiant) Forbes

What size

are the PEX lines connected to the old steel mains?



Gravity systems prefer larger pipes because there is less pressure drop.  It's like approaching two tunnels going the same direction when you're driving.  Would you want to go to the small tunnel congested with traffic or the larger one that has just a moderate amount of traffic?



You might consider switching to a pumped system and installing balancing valves on the supply pipes to restrict flow on the larger pipes in order to promote flow to the smaller ones.

Ironman

Gravity System

Alan's right. The pipe sizes to the new rads must be the equivalent to a similar size old rad. Usually, 1" or 1.25".



Also, the upper floor rads must be connected to the side of the horizontal mains, not the top. This is done to direct hot water to the lower floor first and prevent over-heating the upstairs.



Click on the "Systems" tab above. Then go to "Hot Water". Then to "Gravity Systems". Dan has a excellent article there.

sovavto

possible resolution?

Thank you for the replies. Yes, the content on Dan's site about Gravity Systems is great. I wish I read it before I hired the plumber who turned out to know as much as I knew about this system, if not less.



The size of the old mains to which the 3/4" pex is connected is about 1.25 or 1.5".



I see that 3 things are being suggested. I'd like to try and clarify a few details if I can:

1 - adding a pump (can it be added for just the 2 problematic radiators, or the entire system)? I'd hope to avoid the pump if possible.



2 - adding balancing valves to larger pipes to direct more flow into the smaller pipes. could this option work on its own without converting to a pumped system? if the valves are added, do they need to be added to *all* larger pipes in the system, or just those that are in close proximity to where the pex is connected to the old mains?



3 - checking that the 3rd floor radiator draws from the side of the horizontal mains, and 2nd floor one draws from top. Basically, the section of horizontal mains to which both new pex supply lines were added terminated in a supply for a single radiator, and this single (original) supply that is at the end of this radiator went up from the main (basically a 90 degree elbow at the end of horizontal run). in other words, I have two T connections made about 2 feet apart for the new pex supplies, and an original 90 degree elbow 3 feet further at the end of horizontal run. Would it make sense to perhaps switch these around so that the end of the line would be made to connect to the narrower pex, and the original radiator (that used to be supplied from the 90 degree elbow at the end), would instead draw from the side of the horizontal mains? I'll try to get a photo of this segment to clarify what I mean.

Ironman

Answers, I Hope

1. The whole system would have to be pumped.



2. Balancing valves would be necessary on each riser, unless you piped the new rads back to the boiler and then split the system into two or more circuits. The new rads would have their own circuit and pump and the old would have their own circuit(s) and pump(s). You could then balance each circuit by pump sizing/speed and valves.

3. I'm not sure that I understand what you're asking here ( I'm tired too). Try a pic or posting a drawing. I'll check it tomorrow when I'm firing on all cylinders.

sovavto

picture

Thanks Bob.

The attached picture shows the segment in question.

S1 - PEX supply for 2nd floor new radiator

S2 - PEX supply for 3rd floor new radiator

S3 - supply for 2nd floor original radiator

==========

What I was asking in my previous question #3 was whether S3 could be changed to be 2nd floor new radiator (end of horizontal mains, going up), S2 could remain 3rd floor new radiator, and S1 could be made to supply 2nd floor original radiator with the supply line comming off to the size of the mains..

The idea being that sideways S1 using original 1.25" diameter would offset S2 and S3 connections both of which would be connected from the top of the mains, but use the new 3/4" pipe diameter.

icesailor

Non heating radiators:

You're right, the guy didn't know what he was doing.

That looks like a new pipe that he took the radiators off.

Your problem can only be resolved by someone who knows what they are looking at and know what they are doing. Even if the connections were made with the old connections, hot water should still flow to the radiators. They just may not get hot or barely warm. Because the water doesn't flow at to the radiators, I think that something else is happening. 

If there is a pump, one of those fittings should have been a Mono-flo. You said it isn't pumped. Gravity systems were really direct return systems. If both sides of the radiator were piped on the same side, supply or return, it won't flow. But first, someone needs to look at it. Or you need to post more pictures.

My opinion.