Once again an RV makes an easier job much more difficult. After finally getting the HVAC system to call for heat on both zones, I discovered the circulating pumps were siezed. When I went to replace the pumps, I found the hydronic fluid plugged and gross. So join me as I flush the system repeatedly and fill it. This was a HydroHot HHE200 but should be true for all AquaHots and HydroHots. Thanks!