First, there is a 3 speed fan switch on the cluster in the kitchen area. Off, low, medium, high. Make sure that switch is on when thermostat is calling for heat. Second, on top of the Aqua Hot, there are check valves that get stuck closed occasionally. Tap lightly on the check valves of the lines that are not hot. A screwdriver handle or wood dowel that won’t damage the check valve. Lightly is the key word. Try that first. If no joy, then make sure pumps are turning inside Aqua Hot housing. This involves removing part of the surrounding cabinet of the unit itself. Hope this helps, good luck!