Hoffman Differential Loop device

roland Chicopee,MA

New boiler was installed.Hoffman device was cracked ,so the heating man removed it from system,now we are not getting heat through the radiators. Was this device a vacuum creating device?Can we do something to make it work? this is a 2 pipe system with thermostatic traps on the return end of the radiators.Any help would be great.

Mark W

Probably a main vent...

If the air can't get out, steam can't get in!

Have a properly sized new one installed; do *not* let the contractor crank up the steam pressure in an attempt to get heat to the radiators.

Jamie Hall

Oh dear...

The Hoffman Differential Loop deviced was -- and is -- an amazing bit of very simple plumbing. Well... perhaps not as simple as it looked, though. Well described in Dan's book (Lost Art). What it did, fundamentally, was ensure that condensate could -- and would -- return to the boiler while, at the same time, it kept steam pressure out of the mains.

Depending on exactly how your near boiler piping was replaced when your heating man took it out, there are any number of things which could be causing no heat. While it could be a main vent problem (the heating man did put a new one in, didn't he?), it could also be that in some way the near boiler piping was reconnected in such a way as to allow boiler pressure to get into the dry return line. In fact, the Hoffman Differential loop did look as though there should be a line from the steam header to the dry return -- unless you looked inside it -- and it is possible that things got hooked up a little funny.

Assuming that it can't be replaced in kind, which would be the ideal thing to do, can you post a sketch of the near boiler piping, or a picture? Then Noel or Ken or Mad Dog or Steamhead or one of the real experts can help you!

Steamhead

I'll bet

the contractor didn't vent the dry return and that's what's causing your problem. But, take some pics of the piping around the boiler where the Loop used to be and post them here. We'll let you know for sure.

Thanks for the kind words, Jamie!

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