I have an oil fired hot water system in my house (about 10 years old)
and everything up to this point has been fine. My water is supplied by
Recently, I've notice big "spikes" in my water pressure. Sometimes
when I turn on the water the water seems to come blasting out for the
first few seconds. In addition, the last few days I've notice some
water coming out ot the pressure relief valve on the hot water tank.
These things seem to happen most after using the a lot of hot water,
for example when someone takes a bath.
My system has a thermal expansion tank, but I'm beginning to suspect
that it might be bad. Does anyone know how to test these tanks. Also,
is it something that I can replace myself (I'm fairly handy). It looks
like it simply screws into a fitting in the water line?
Thanks in advance.
Seems you've lumped heated tap water with water used in a closed loop
to heat the house. Split them in your thinking, and take another look
at the systems.
One possible cause of high pressure of domestic hot water: use of lots
of heated water, which is replaced by (obviously) cold water. This is
now heated and expands. Being trapped in a closed volume between
check-valve and faucets, the pressure rises. Also, the water in the
non-house-heating part of the furnace may be over-heated (like, from
extended burner run-time heating house), or the water may have lots of
dissolved gases which then outgas at elevated temps.
There are lots of DIY books that'll get you oriented.
I'm going to take your words literally Joseph and understand that what
you are asking about is an oil fired hot water heater, and NOT an oil
fired hydronic heating system which warms the living areas.
If I'm reading you correctly then it does sound like you have an
expansion tank hooked up to the DHW system and that tank is likely
The simplest older expansion tanks were just that, a tank with an "air
space" above their typical water levels. They usually have something
which looks like a Schraeder valve (tire valve) on top through which you
can pump some air with a bike tire pump to replace what has been lost
through absorption in the water.
Newer style tanks use a rubber diaphragm inside to separate the air from
the water to avoid losing air through absorption. That kind of tank will
hold its air space for years, until the rubber finally fails and
develops a tear, then the air space will decrease slowly through
absorption in the water. Those tanks usually also have that Schraeder
valve on them through which you can periodically pump some air in until
you get tired of doing that and decide to bite the bullet and replace
With regard to "the test" grab a bike pump and squirt some air in. If
the "high pressure" problem goes away, you've got your answer.
HTH and Happy Holidays,
Thanks for the info. The thermal expansion tank has a schraeder valve
on the bottom, so I assume it's the bladder type.
When I put a pressure gauge up to the tank it doesn't show any
I tried to just push the valve in to see if there was water leaking
out, but it's dry.
So I plugged in a bicycle pump and tried to pump it up to 40 psi. But
as soon as I disconnect it and recheck the pressure it seems like it
hasn't "taken" any pressure.
Do you have to turn off the water and take the tank off to recharge it,
or can you charge it while it's in the system?
I'll go along with that and am embarrassed I didn't think to mention it.
If the entire system and the expansion tank are all filled with water
and there's no way out for it, when you try to pump in air there's no
place for the air to "fit" other than the tiny bit of volume gained by
further "stretching" of the plumbing and water heater tank. (Water is
essentially incompressable for practical purposes.)
If you want a quick try at it without removing the tank, shut off the
water supply to the water heater and open a hot water faucet. That
should let you pump in some air in situ and let you see how that works
for you, but I bet you're gonna have to remove that tank eventually anyway.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.