Why won't this radiator get warm?

Eric Scheidler

This radiator in my home's vapor system never really gets warm. Gets a little warm at one end, where the valve is, but the heat never gets more than a few fins along.



Looks like this was originally used in a hot water heating system. The valve is down at the bottom, rather than at the top:



When I moved in 15 years ago, there was a bleeder attached. I removed it when I repaired the whole system (half the radiators never got warm back then -- long story), and plugged it:



Finally, the trap looks different from all the others in my system:



I'd really love to get this radiator cranking. This room happens to have 11 windows! (Half of it was once a 3-season sunroom, which at some point was incorporated into the room). Gets really cold in there.

Don't ask why it's taken me 15 years to try to fix this thing!

I'd be grateful for any insights you guys can offer. Back in 2005 when I moved in and had to get the system working in the first place, this forum was a life-saver. Hoping for more of the same in 2020!

Thanks!

-- Eric

Fred

The trap, on the end opposite the inlet valve may be failed closed. Air can't get out through the trap into the return pipe. If you can get the cap off, you can get new guts for it if you can find a name on the top.

Jamie Hall

That looks like a Hoffman 8C. Replacement parts are easily available -- try Barnes & Jones or Tunstall for a replacement cage unit. State Supply has them.

Eric Scheidler

Thanks, guys. Just checked, and yes, this is a Hoffman 8C.

Is there a way to diagnose whether the trap is failed closed, apart from replacing it (or just the internal parts) and seeing if that works?

Also, is this the right kind of trap for my system? The reason I ask is that when I moved in, they had a pressure stat on the boiler, instead of a vaporstat -- one of several indications that someone who didn't understand vapor heating worked on the system.

Finally, should I repipe the radiator such that the steam enters from the top instead of the bottom?

Jamie Hall

Yes, the 8C is fine for a vapour system. As to diagnosing a failed trap, you have the classic symptom: no heat. There are other possible reasons for no heat, but that's the most common.

Eric Scheidler

Thanks for the follow up, Jamie.

It sounds like it can be difficult to get the caps off these things. And I see recommendations to replace the cap when doing a repair. Any tips about getting the cap off?

I'm wondering if I should just buy a whole new trap. At State Supply, it's only about $15 more for a new 8c than for the cage unit and cap.

(BTW, does "Br. Jamie OSB" mean you're a Benedictine? My dad was at St. Meinrad back in the 50s. . .)

Jamie Hall

Yes, getting the caps off of those things can be difficult. A six point socket which actually fits, and a backup wrench, will usually do it.

The trouble with buying a whole new trap is in getting the union with the radiator to fit properly. Sometimes you get lucky... sometimes not so much.

And yes, an Oblate Brother of the Benedictines. I came to it rather late -- it's a long story.

Eric Scheidler

Success! I installed a new Hoffman 8c, after finding it would take a while to get a cover, and I would need a special tool to remove the cage unit. Fortunately everything lined up nicely, and the radiator is now getting great steam:

Fred

Great!

archibald tuttle

the only thing i have to add to the happy completion is that @Jamie Hall is right that a six point socket and a backing wrench on the body or lower hex boss will usually remove the caps. I've had success with an 18V cordless impact wrench driving the socket as well which tends to impart less torque to the trap body based on its impact action versus the continuous torque of a 3/4" breaker bar or some such and have had 100% success as long as I get a socket that fits well. (actually some of my large sockets are 12 points but the good fit has not made them prone to take off brass corners).

when the symptoms are of failed-closed trap i open the cap and remove the element to insure the rad heats up. I do tend to keep extra caps around if they match across a system if something goes wrong and because some of the traps have an integral element w the cap so a cap with the unit removed is handy for noting the the radiator heats if the failed trap is removed. And, mildly dependent on other system characteristics I have successfully limped along with no cage unit in the trap on a rad or two while awaiting new caps and cages without significant steam in the returns.

Big Ed_4

That is big radiator , does it do the job ? You may want to leave it alone .