Hi,
I have an older 3 family house, which has had some updates to the plumbing. A recent problem: the tub and faucets in the second floor units have no pressure and lots of banging when turned on. It seems to mainly happen at night. Someone suggested that we have air in our water heater. How can we fix this?
Thanks!

I don't see air, I see debris in the pipes and valves. You going to have to disassemble and flush them all out.