Take the Piccadilly line from central London straight to Heathrow; it’s affordable, frequent, and stops at all terminals

https://donovanoxeu003.trexgame.net/how-do-i-get-to-heathrow-terminal-four-step-through-step-routes-and-tips

Take the Piccadilly line from central London straight to Heathrow; it’s affordable, frequent, and stops at all terminals, though it can be crowded during peak travel times.