Musical Cold Radiators (Steam)

Noel

I had a problem once that this one reminds me of (even though you likely will tell me you don't have TRVs) in a building that had over 100 radiators in it over 5 floors.

After the radiators ALL had Thermostatic Radiator Valves installed (in a building that still has most of a Vari-Vac system in it), there would be radiators that would behave as you describe.

It was in the milder shoulder season (spring), and each day, the problem would move to a different room. It was bizarre.

The risers went up 4 floors and served radiators left and right of these risers. Every other room would have a pair of risers in the corner.

It had worked fine all winter. Now, I could expect a no heat call in the front half of this building EVERY morning, but never to the same room.

Here's what we found. The top radiator on the riser USED TO vent the riser when the steam came on. Now there are TRVs everywhere. The riser would work GREAT until a TRV closed off tightly (warm out). Then the steam would cool off at the TRV inlet, but no air could get in, and the water that formed just hung there at the top of the riser. More water formed from the TOP, down. Once 2 or 3 feet of water column would form, and the steam wouldn't push it up through when the TRV opened. That slug of water would form all of the way down to the main in the basement.

Later the boiler would shutdown as the day warmed up, and ALL of the water would fall back to the boiler. The next day it would be a different riser flooded.

I put a tee beneath the top TRV on each riser, and piped a radiator trap from the tee, and into the return on the other side of this same radiator. Top of riser trap, like an end of main trap.

Now there's always steam at the top of the risers.

Noel

Karl_7

Musical Cold Radiators (Steam)

Occasionally, one of our second floor radiators will be cold. This doesn't happen all the time, and the cold radiator is not always the same one. It happened again today - this morning one radiator was cold when the heat came up, this afternoon it was a different radiator.

I did replace the thermostat yesterday with a new programmable thermostat (Honeywell RTH7500D), but the previous thermostat was programmable and this happened occasionally with the old thermostat also. So, it's unlikely this is the problem, but I figured I should mention it.

The system is one-pipe steam. The boiler is formerly oil-fired, but the burner was replaced with a gas burner some time in the past (I don't know how long ago). We did have someone in last year to check the burner, and we were told that it was fine.

Any suggestions? What should I be looking for?

Unknown

Here's what it looks like

Noel

Christian Egli_2

Nose blowing or CPR, it's a fine line

Thanks Noel for the beautiful explanation of what a crossover trap does. I think that's exactly what you added to the two pipe system and it's not just main venting, it's flow venting like in sewer lines.

Amazing experience you had there. Thanks for sharing.

This would translate for Karl and his one pipe system in a main venting problem. So, look for end of main vents (you need them installed if there are none). Also, all this could be as simple as old radiator vents that stick shut sometimes or that remain water logged sometimes, thus trapping traveling system air inside. Air is always cold.

Next time one radiator remains cold, try mouth to mouth resuscitation on the vent by blowing into it, possibly snapping it open and blowing it clear; then watch it breathe again -we hope.

If the radiator then gets hot: new vents are in order. I hope it's as simple as that. Let us know.