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
other Brands out there and the
work much the same.
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
get much larger but this page is
for Home owners.
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.
get into how to replace it, I
should ask, does it really need
to be replaced?
If it is leaking, then it's
simple, It needs to be
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.
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
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 clicking here
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 of water.
This is also a #30 tank And
this would also be easy to
Ok So now we have determined if
we should replace it or not and
what type of tank we need. So
lets replace the thing already.
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
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