The heater control valve is located on the driver side of the engine bay. It sounds to be similar symptoms to my issue. Probably a bad heater control valve. The hoses going to the passenger compartment from the heater valve will en be hot due to proximity of the engine. If the engine is at full temp then the hoses will be about 100c so hot you won't be able,to,touch them for more than an instant. I'd bypass the valve with a stint to see if your heat problem goes away.

Here is a troubleshooting guide. BMW and MINI DIY – No Heat – Diagnosing Heater Problems How To Diagnose | Bavarian Autosport Blog