Be sure your auto feed valve and feed are off, set to correct pressure
10-12 cold, drain expansion tank and see if it climbs again. Does the
expansion tank have an autrol valve, it could be bad. Ck the lb rating
on the relief valve, it should be 35lb. Dont let it go to 50lb.
Post at " The Wall" for alot of boiler people and good advise. Alt hvac
is a joke.