Noticed last night the boiler water pressure is just below 10 psi. I used the fast fill lever to bring it up to 20 and a few hours later it was down to below 10 again. When I had added some water I could hear the vent valve and some water and air came out. When the pressure was low I watched the water meter for 5 minutes and it didn’t move. Today I checked the expansion tank with a tire gauge and there no reading. I tried add a little air with a tire pump but was unable to force air in, I pushed on the valve with my finger and nothing came out
Am I right in assuming that the expansion tank needs replacing? It’s probably between 7 and 10 years old.

 

Checked boiler pressure after heat cycled on and boiler brought temp up to 180 and shut off. The gauge reads just under 30 pounds. Still no pressure in the expansion tank.

 

Yep, time for a new one. When changing, install a ball valve between the tank & the boiler. It will make changing the next time a snap.

 

I just installed a new Extrol expansion tank for my boiler because the old one was filled with water (you can just tap on the side and you'll know). Beware when you unscrew that baby you better have a hold of it because it'll surprise you by how heavy it is. Also when you install the new one make sure its got air in it. I guess most of them come pre-filled. Mine was supposed to have 12-15 lbs. I hope this helps you...good luck...