My Dunham/Bushe residential boiler is a hot water boiler with a forced
hot air central heating system. It has been running at a high pressure
(30 lbs.) and this is causing the pressure relief valve to release
water. I drained the expansion tank (which was full) by shutting the
feed and opening the drain valve. It is an old system with no
compressed air in the tank, which I believe does not have a bladder in
the tank. It does have a shut off valve below the inlet to the tank
and a drain valve with a hosecock connection on the opposite side. The
inlet and drain are both on the bottom of the tank. After I drain it
the system functions fine for a day until the pressure builds up and
the tank is full again. I think I am bleeding it right, or am I? The
pressure relief valve does go off due to the high pressure, but does
seem to seat well after the pressure goes down. After reading some of
the postings on the board, I also thought that the temperature setting
on the aquastat may be too high. It is currently set at 160 as the
high and 130 as the low with a 10 degree differential. What would the
correct temperature setting be?
I would appreciate any assistance. Thank you, MRnice
I think you have a good understanding of the system and
how that ancient exp tank works. Should work with those
temp settings OK.
It's possible that an automatic fill valve from the
incoming water supply is leaking and refilling the system,
causing the high pressure. Find a shutoff valve and close
it to find out.
I am emptying the tank again to make sure it is totally empty. I think
air will enter through the drain valve into the tank, which should be a
good thing if I understand how this tank works. I will look for a
valve on the autofeeder, I know on a steam system it regularly fills
which you can see in a guage glass. I am not as familure with Hot
water systems. I guess too much water would push up against the
pressure relief valve causing the 30+ lb. reading on the guage too. Of
course, I know this is a more difficult fix. If I wanted to run the
boiler without the feedwater regulator for a while, how often would I
add water to the boiler? How would I know when it needs it? Thank you
for your suggestion, it seems like the only other reason for high
pressure. The stack is clean, relief valve seems to work only at
preset 30lb. and the temp. is not too high. Do these boilers require
any cleaning , chamber, etc.? I have changed the oil filter, replaced
a bad ignitor last season (my first season in home), and cleaned the
flame scanner eye as well as changed the nozzle. Could lack of prior
maintenance have caused sediment buildup to produce a high stack
pressure causing a problem? Thank you for your advice, Ron
Unless there is a leak, that boiler shouldn't need
feed water except in rare cases.
Oil-fired does need annual maintenance for cleaning
and combustion air setting, etc. But that's not
part of this problem.
That has to be a cast iron boiler, so there are no tubes.
Get the pressure under control and see if there is any
evidence of leaks.
if the expansion tank is filling with water when the system is in
operation , then the tank has an air leak and air is leaking out,
letting water in... then when the tank is full of water, the pressure
will build excessivly when the water is heated..
the air leak may be very small, like a tire with a small leak...
Each time I emptied the expansion tank, I opened the inlet valve and it
seemed to fill. I closed the automatic feedwater regulator and the
tank did not fill when I opened the inlet valve this time. I emptied
the remaining water in the tank and put boiler on. My well water pump
had a problem right before this happened and the water to the house was
cut off for a while. Maybe some sediment ended up in the autofeed reg.
when water was restored causing it to stay on. I think you hit it on
the head with the feed water problem. Is there any way of cleaning the
regulator to possibly repair it before going out and buying a new one?
Auto feeds go bad and can be innacurate new. Turn it off and the
supply, filling a boiler for my house is a once year deal, I have 3
stories and keep 12-15lb cold. some systems need a bit more. Your
pressure relief leaking is warning your pressure is to high, eventualy a
boiler leak can develop. Im just a homemoaner here, no pro but I would
call the manufacturer of the boiler and find out operating pressure
guidelines, less is better for boiler life. I would wait till cool and
drain water till its 15lb, keep the water fill off and see what happens.
If you have 1-2 story house 15 may be not needed as I say I run 12-15 on
a 3 story with boiler in basement, 4 levels, old and new boiler run the
same. If no heat gets to upper radiators add a lb when Cold and bleed
running. A too small an expansion tank can cause the same symptoms,
increasing pressure when hot. Filling a boiler constantly is not good
for a boiler as scale develops , reducing efficiency and life, if it
knockc its got scale.
If it is the same as my Watts fill valve and safety, it is a piece of crap
and you toss it away. If it was sediment under the valve seal, it would
probably be flushed out by now. My heater has had four Watts fill valves in
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