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

https://arthurrops446.wpsuo.com/national-rail-to-heathrow-routes-transfers-and-tickets-explained-2

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.