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

https://arthurrops446.wpsuo.com/london-to-heathrow-transport-best-route-by-time-of-day-and-budget-1

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.