1151 code

Getting 1151 code after I changed inverter coolant and engine coolant.
Thinking I must have air in the engine/storage tank coolant loop.
I was patient on the refill procedure. Drained out 1.5 gallons of engine coolant by opening yellow petcock valve under storage tank. Refilled coolant into radiator with bleed valve opened while watching for air release and intermittently running pump. (Not sure what pump is running, engine water pump or storage pump). I pulled the blue relay on the right and shorted out top two contacts with amp meter connected. Meter fluctuated during refill, but know reads 4 amps consistently while shorted. I clear the code with a bluetooth obd reader. Check engine light comes back with the same 1151 code.
Radiator and overflow tank are full. So I try to purge air again - connect overflow tube and open the bleed valve, short out out the relay socket, look for bubbles and watch meter. Consistant 4 amp reading, coolant flows slightly from bleed valve and very little if any air bubbbles appear.
What am I missing here? I did replace the coolant sensor from underneath the tank as the old one had exposed contacts.