I have a T991A modulating stat controlling a honeywell fluid power gas valve type:v9o55a 10552. problem i'm having is the t991a is set for 70* with a 3* diff. the gas valve bottoms out on low fire then goes out on the fire eye. i've tried to adjust the low fire dial inside the gas valve but no luck.
i've moved the stat setting higher with a 15* diff and it doesn't bottom out. i'm almost certain i have a bad t991a stat? and what do you guys set your diff setting for on that type of stat? this is a direct fired mua.