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
a well.

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.