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 ¼ 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
That's correct. 20 psi should be good for damn near 40 Ft
elevation. Of course, it *is* possible that the gauge
With 20 psi at the boiler, you should be able to get
a powerful stream out of the highest rad vent.
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.
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.
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).
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?
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.
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
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.
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