Need more information... Have you looked at the unit itself for fault lights? Check the zone board for red lights, red light normally indicates blown fuse. Fuse is 10 amp. If fuse is good, check for voltage to the circulation pump. If good voltage change the circulation pump (in a pinch you can turn on the "By Pass" switch which will circulate fluid throughout the system.) If the loop pump is running, but you're not getting warm air at the vent, "smartly" tap the pump check vale to un-stick the valve.
Ken & Anita
2011 Newmar Essex, 45'- 4522, Cummins 500 ISM, 2013 CRV, RVI2 Brake with TPMS