Honda getting hot. All air drained out of water system

Looks like you have a leaking head gasket or cracked head. You can buy a head gasket leak detector kit that will let you know if there is CO2 gas escaping through the radiator. I think that it is this gas leak that makes it look like your radiator is boiling.

Change thermostat first! Then change temperature sender!

sounds like you have a head gasket gone bad. these cause overheating and the compression gases cause the air in the system and to boil out of the system. as such will cause the heater not to blow hot air, as steam will contain heat very long. the white smoke upon start up is a tell tale sign that the gasket has blown and needs replacement. have a head gasket test done. it could also be a cracked head or even a block, but head gaskets are a problem.

You would probably be better off replacing the belt and pump again since the labor would be next to nothing.
I would want to test the cooling system for exhaust gas and try to verify the head gasket is actually leaking next.
Are you loosing coolant into the cylinders ? There may be something else causing the engine to run hot such as exhaust problems.

check radiator is not blocked, check air can pass through radiator (fins not blocked with debris) check that there is no airlock in system. is header tank being pressurised when engine running ( remove cap and start engine, look for bubbles in header tank). If bubbles then you need to check head gasket or even crack in head or cylinder walls. Presume you fitted the thermostat in the right way round. if you have boiled the engine since fitting the thermostat you will probably need to remove it (maybe see if it boils without it fitted) and possibly replace it again. (drop in hot water and see if it opens, if it doesn't then replace it)

Ususally when the heater blows hot air only when the car is at hight RPM is because low coolant in the system. It sounds like a bad thermostat . In the worst case you need to do a diagnostic check to the head gasket. Because the first thing to get blowen out when the car over heat are the head gasket.

may not work but try undoing the clip on the highest hot hose to vent any trapped air.

most common fault,have you bled ALL the air out of the water system?????

It's possible that the thermostat is defective.
Also check that the overflow hose and resivour are not cracked.
Check the engine oil, if it looks foamy then you may have a cracked head.