Radiators cold pressure OK


have a very old (I'm guessing 45 years) oil fired hot-water boiler. My problem is two radiators (not steam type) on my second floor (bedroom & bathroom) don't get hot. If I crank up the thermostat to 76 degrees, one of the radiators will get warm about of the way up (I normally keep the thermostat at 68), the other remains ice cold. There is a large radiator with an automatic bleeder on it which throws off a lot of heat in another bedroom on the second floor. I tried turning that radiator off- didn't help. The bathroom radiator with the automatic bleeder is cold. The pressure on the boiler show 20 when cold and 23 when hot. When I bleed the bedroom radiator, air comes out but no water. All radiators on the 1st floor have been bled & water comes out. Last winter, the pressure was at 10 & I had the same problems, so I put on an automatic bleeder on the bathroom radiator to no avail. Any suggestions appreciated.
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lacnob wrote:

Not enough boiler pressure.
Have another look at the gauge. Is the "20" in Feet? That's probably just shy of what's needed to get to the bath.
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This a troll or a total idiot. The only way the Second floor can vent heat is if its a steam system with a bad vent. But HW doesnt have Auto Bleeders. So By By Troll, or moron
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Speedy Jim wrote:

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Speedy Jim wrote:

Thanks for the input. The 20 is pressure. The "red zone" starts at 30. From what I've read, 12 to 18 PSI is adequate so 20 to 23 should be more than adequate.
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lacnob wrote:

That's correct. 20 psi should be good for damn near 40 Ft elevation. Of course, it *is* possible that the gauge is inaccurate.
With 20 psi at the boiler, you should be able to get a powerful stream out of the highest rad vent. Jim
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Speedy Jim wrote:

Could it be that on the cold radiators the bleed valves are slightly corroded so air might be getting in through the valves? Should I try radiator blanking plugs?
lacnob
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lacnob wrote:

No. With adequate boiler pressure, the bleed valve will always have pressure behind it trying to force water out, so air can't get in.
If the boiler gauge is accurate, then maybe there is a large accumulation of air in that part of the system that you just haven't bled off yet.
One thing that *can* happen is if the boiler pressure drops a lot (like at night during shutdown), the system will have a vacuum at the highest rads and air then *can* be sucked in. Jim
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Speedy Jim wrote:

Maybe on to something here. I do have a programmable thermostat so at night the temperature drops down 5 degrees lower than during the day (5 degree offset) and I'm assuming the boiler pressure drops a bit too ( have seen it at 19). In the morning when the boiler goes back to its higher pressure is when one of the cold radiators sometimes gets a tiny bit warm on the bottom. I did notice the very first time the boiler turned on during the season, the radiator got hot half way up ! I'll try a 10 degree offset tonight and see what happens. Thanx.
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lacnob wrote:

Try the experiment, but the system should be able to handle long periods of no-fire without great swings in the pressure. The expansion tank should be absorbing most of the pressure difference.
Even at 19 psi, there should be enough "head" to keep pressure at the highest rad (in a typical house).
Jim
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Speedy Jim wrote:

I tried the 10 degree offset. A whole lot of air came out of the radiators but no water & radiators are still cold. I did notice the hi-low water temperatures for the boiler are set at 160/180 however the water temp on the boiler never seems to go over 160. Perhaps the stats are off. I'll move them to 170/190 which will probably bring the normal temperature to 170 or should it be higher? Also, would draining the expansion tank help?
Lacnob
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lacnob wrote:

The temp won't matter as far as getting water to the rad. Draining the exp tank (old fashioned non-bladder type) will help reduce pressure swings but it seems to me you need *more* pressure to begin with if you can't bleed off water from that rad. I'm assuming that, if you leave that bleeder open, the air escapes and finally stops and after that....nothing.
It's probably "inconvenient" to replace the gauge (drain whole system) to see if the calibration is off. As a quick test instead, crank the incoming regulator or feed valve up a notch. It's also possible to screw a calibration gauge onto the drain cock as a check.
Jim
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Speedy Jim wrote:

Yes, if I leave that bleeder open, the air escapes and

"As a quick test instead, crank the incoming regulator or feed valve up a notch"
I recall when I had a boiler tuneup, the man said two blue handled on/off faucet-type valves had been installed, sometime, just above the two old "bell shaped" valves probably because one or both of the old valves were not working. There are two lines coming off the city water line. One leading into the boiler and one leading to the bell shaped valves. I'm assuming you're suggesting I let some water into the boiler? How do I know how much? Replacing or calibrating gauges- no can do, but thanx Jim, for the help so far.
Lacnob
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lacnob wrote:

The one leading direct into the boiler allows you to feed water to it manually. Open that one and watch the gauge. Let it go up 3 or 4 lbs and then see if the top rad will bleed water. Repeat as necessary. <g>
The bell-shaped valves are an automatic pressure regulator feed device. Supposed to sense the boiler pressure and feed fresh water as needed. They don't always work reliably.
Jim
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