I took the expansion tank off and drained the water from it. It was about 1/3 full. I recharged it to 12# and reinstalled it. I filled the system up with water and now twice Ive had to release some water, about 3/4 of a gal at a time to bring the pressure back down. I set the aquastat to 160 but it keeps firing till about 180. The differential is set for 15#. What pressure should I be looking at if the water is 160 degrees? Is there an acceptable range?