Furthest Radiator Not Really Heating But Inlet Pipe is Hot...Need Perspective

honeydo · January 2016

Hi, need a little direction. Single-pipe steam piping from 1940 but last owner replaced boiler. Works well in all rads but the furthest. Measures approx. 3'Lx18"Hx 8"D. Issue came to forefront when prolonged gurgling whistle from air vent woke up the people sleeping in the room. No water hammer, just the noise from the vent. The supply pipe is hot, the inlet shutoff valve valve appears to work and the pipe from the valve to the rad is hot. The first section gets warm, but that's it. I removed the air vent altogether to see if that was the problem. After turning the thermostat up and waiting maybe half an hour I finally got good steam (with the vent out). Shut the valve, installed the vent and re-opened the valve. The vent shut but once the thermostat was turned down we go back to square one. Read We Got Steam Heat and am resolved to make this work. The vent is new, #11 Vent-Rite. The rad has pitch towards the inlet. When The rad was cold, I opened the fitting to the inlet valve and drained out maybe a cup and a half of water. What would inhibit the steam from continuing to fill the radiator? What can I do about it? Thanks.

KC_Jones · January 2016

Bad pitch on the pipe feeding the radiator. Have you checked the pipes in the basement? Also not enough main venting can cause this situation. The other rads will get steam and by the time it gets to that one the thermostat cuts off and no steam, then the cycle starts again. How much main venting do you have?

Fred · January 2016

Since you say the radiator is already pitched towards the inlet pipe, I'm in agreement with KC. The horizontal pipe to the radiator is probably pitched the wrong way and holding water. If this is a first floor radiator, check that pipe in the basement and make sure it is pitched back towards the main. If this is a second floor radiator, try to lift the radiator a bit. See if you can get a quarter inch or so lift on the inlet side of the radiator and then re-pitch the far end of the radiator towards the inlet pipe. Raising the radiator should help pitch the pipe under the floor.

honeydo · January 2016

Thanks guys. Shimmed the rad up 1/4" more overall and was able to raise the end of the supply coming out of the floor slightly as a result. The issue is on the second floor so almost all the piping is hidden. With a 4' level and no sag in the middle sections of the rad there is about 1/8 of a bubble pitch on the vent side. Do you recommend more? KC, you asked about vents. There is a large vent on each of the mains right at the end. They hiss when I turn up the thermostat a few degrees, but if it stays set at a steady temperature I am not hearing them even though the boiler turns on regularly throughout the day. Do they only vent substantially when you try to raise the temperature or should the be venting every time the boiler turns on?

Abracadabra · January 2016

pics of main vents.. pics of radiator

Fred · January 2016

The vent side of the radiator should be the high side of the pitch. Did raising it help any? Main vents will vent every heating cycle. You may not have enough vents on the mains. How long are the mains and what diameter is the piping? A good rule of thumb is the equalivent of one Gorton #2 vent for every 20 feet of 2" main.

Jamie Hall · January 2016

Main vents do vent on every cycle, but... on a relatively short, light cycle such as maintaining temperature, it is quite possible that you won't hear them at all.

honeydo · January 2016

Ok.
After lifting the rad and rechecking pitch, heat will come but still only if I push the thermostat up a few degrees. Still sputters and whistles though, not the clean quick hiss and click of the vent. The rest of the rads in the house get quite hot in the meantime. There is about 1/8 of a bubble pitch towards the inlet. Should I try for more? Can one over-pitch? Keep raising?
The inlet valve closes, but do they ever not fully open or not drain the condensate? What if the pipe under the floor has sagged? Any other troubleshooting you could recommend?
Trying to assess the venting. Just to be clear, when you say 'vent the end of the main', are you saying that there should be more vents than the ones at the returns? There are two V-R #35s visible, each one just before the return lines drop back down to the boiler's wet return. Can't see any other vents besides the ones on the rads, and a drop ceiling hides most of the piping in the basement. Also, the #35s don't seem to ever close, just vent air then blast steam onto the underside of the first floor. Not sure if they are original or if the last owner replaced them with the boiler. Of course, they are not budging for inspection but before I get 'more convincing', they should close, correct?
Getting some pictures and technical info together, thanks for the patience and knowledge. This is very helpful site.

Fred · January 2016

Vent-rite #35 have about 1/10th the venting capacity of the Gorton#2 ve for a main. You need to replace those with Gorton #2's. You need about 1 Gorton #2 for every 20 ft. of 2" main. Until you get the mains vented right, you are wasting your time tryiing to make a radiator at the end of the main heat properly.
Yes, Vents should close when steam hits them.

BobC · January 2016

If the vent is hot and not closing it's failed and has to be replaced. The 35 is a fairly slow vent, you probably should have a lot more venting on the mains. Do you know how long the mains are?

If the radiator is pitched and the piping in the basement is also pitched and doesn't have any sags then there might be a horizontal pipe between the ceiling and the second floor. Try lifting the entire radiator up by 1/2 to 3/4" and see if that changes things.

Bob

Furthest Radiator Not Really Heating But Inlet Pipe is Hot...Need Perspective

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