Why does my furnace need an
When water heats it expands and
water can not be compressed, so
without an expansion tank
installed, pressure will build
and cause the relief valve to
The boiler expansion tank
absorbs the expanding water by
allowing the air in the
expansion tank to compress, this
prevents the pressure from
building and allows the boiler
to heat and cool without too
mush pressure building up.
Removing the furnace relief
valve from the boiler or
plugging it so that it does not
leak is a very bad idea, this
can allow the pressure on the
boiler to reach dangerous levels
causing an explosion that can
destroy your whole block. So
don't do that. Now on to the
For the most part Amtrol
expansion tank is the most commonly used
Any Image To See A Larger Image.
There are other Brands
out there and the work much the
For most Residential Boilers the
following 4 tanks are mostly
The # 30, the # 110, the # 15,
and the #109.
Some larger homes need the #60
And they get
much larger but this page is for
So I will not bother with the
Replacing An expansion tank can
be very easy in most cases, but
you are dealing with
VERY hot water and you can get
It may be best to have a heating
contractor do it. but like the one I did on the
Weil McLain boiler,
turned out to be a real pain.
||Before I get into how to replace it,
I should ask, does it really need to be
If it is leaking, then it's simple, It
needs to be replaced. See
Boiler relief valve
If it is full of water, it needs to be
replaced, Tap the tank the back should
sound hollow, if not, it is full. if it
is full, that means it will be very
heavy, So be careful not to let drop on
your fingers when you remove it.
||If there is no air pressure in the
tank. use an air gauge you should have
12 psi. But remember you let air out
every time you test it. If it does not
have 12 psi you can pump it up to 12 psi
with a pump. But this is just a
temporary patch and it will go flat
again. so it should be replaced.
Although a water logged Expansion tank
will cause a relief valve on a boiler to
leak and /or blow off. It is not the
only reason the relief valve leaks and
or blows off.
See why is my relief valve leaking? by
||Note: The #110 and the #30 are the
exact same size tank. but they are not
The #110 is part of a Filtrol System and
only screws into a Filtrol fill valve.
There are 2 types of Filtrol fill valves
one has a valve handle to turn the water
off the other does not. In the pictures
below you will see the both of them.
Filtrol With Handle and Filtrol With
Out Handle. Click on Picture for larger
picture. The #110 and the # 109 will
only screw into one of these valves. The
#15 and the # 30 will screw in to any
1/2" iron pipe size fitting. The #109
and the #15 are also the same size as
each other. but about 1/2 the size of
the #30 and The #110.
||This is a # 30 it screws into the
bottom of an air scoop This one will be
easy to change, but if it is water
logged it will come down hard once you
unscrew it. It is very heavy when full
||This is also a #30 tank And this
would also be easy to replace.
Ok So now we have determined if we
should replace it or not and what type
of tank we need. So lets replace the
||First Turn the power to the boiler
off. Then Turn the water to the boiler
off. Follow the fill valve back till you
see a valve to turn off. If you have
valves on your supply and return lines.
you may want to turn them all off to
prevent draining all your zones.
|| Then hook up a hose to the lowest
boiler drain and relieve the pressure
||If you have to drain the whole
boiler to remove the tank you may want
to remove an auto vent to allow air to
get into the top to allow the boiler to
|| The Rest is easy unscrew the old
one and put some kind of pipe dope or
tape dope on the threads. (only on
the15 and #30) and screw the new one
back in The #109 And #110 do not need
and pipe dope or tape dope they have an
O ring that makes the water tight seal.
ok that's it you are done put the auto
vent back. turn the boiler drain off
turn the water back on
Get the Air out turn the power back
||Before you turn the power back on
and fire up the boiler, be sure the
boiler is full of water and the heat
lines are also full of water.
||You may need to remove air from the
heat loops please follow this link to
remove air from your system
Running a boiler without water in is
will cause damage to the boiler, please
be sure it is full before you turn the
power back on.