Terminal 3-Heathrow Express-Piccadilly Line-London Marriott Kensington

Yes, Heathrow Express runs between the terminals at LHR. By the time you want take it there should be frequent trains( unlike us at 4:30am). You go to the machine to get a free ticket to pass through turnstile.
Sorry, I haven't taken a train into London so can't help with that but the Heathrow Express continues to London although at a high price.

Or you could ignore the Heathrow Express and just hop on the Piccadilly line tube at Heathrow. About 45 minutes, direct to Gloucester Road Tube, no changes.

Considerably cheaper and more straightforward than doing Heathrow Express followed by tube/taxi, as it involves no changes. You’ll be getting on the tube at the start of the line so there’ll be plenty of room to sit with your luggage.

You can’t use an Oyster card for the Heathrow Express - it’s a premium-priced trip that doesn’t go to your ultimate destination.

I temporarily live about two blocks from the Mariott Kensington and you are wasting time transferring terminals at Heathrow.

Here is the easiest and least expensive way to get to your hotel:

From Heathrow Terminal 3, take the Piccadilly line to Earls Court Station. This will take about 40 minutes. Exit on Earls Court Road. Cross the street directly in front of the station (there is a light and a crosswalk.) Turn left. On the next street (maybe 50 feet away) turn right. This is Hogarth Rd. Take this to the end of the street (keeping to your right). Turn left onto Knaresborough Place. Go one block to Cromwell Road. Turn right. Go a couple of hundred feet. Your hotel will be on the right.

The walk from Earls Court station to the hotel will be 5-7 minutes depending on how fast you walk and how much luggage you have. The fare from Heathrow, with an Oyster Card is 1.50 GBP.

The walk from Gloucester Road station is further and will cost more.

Frank talks sense. I don’t know the hotel but found it on the map and it looked to be close to Gloucester Road. But I know Frank knows this part of London well so do what he says!

Wonderful information and much appreciated! Thank you so much for all the replies!

How does Terminal 4 come into this? Is that where your Delta flight lands? i am curious why you asked about the Heathrow Express running between T3 and T 4 ( it doesn't; there is a shuttle that serves T4 to take people to T3). But apparently the Piccadilly Line stops at T4.

My Delta flight arrives at Terminal 3 and I read somewhere that to access the Piccadilly Line from T3, one had to take the Heathrow Express Airport Shuttle (not Paddington Heathrow Express) from T3 over to Terminal 4. (The shuttle runs 4 times per hour between he two terminals.) Then one could jump on the Pic. Line straight to Earl's Court. That's what I came across but glad for everyone's new clarification on how to proceed.

When you get out of customs at Terminal 3, just follow the signs to the Underground. Terminal 2 and Terminal 3 share the station. Terminal 1 has ceased to exist. For now.

On your return, if you are flying out of Terminal 3, the stop will be called Heathrow Terminal 1,2,3.

Got it and many thanks!!

Maybe this is your first time in London? If so, the public transit site Transport for London is useful in planning your day trips. https://tfl.gov.uk/

Google Maps supports a similar function.

TFL will describe the Oyster card. It is an electronic wallet that stores money to pay for transit fees. The rider taps a pad at the entrance to the Tube, and then again when exiting. The fare for the ride is automatically deducted. They are available at the airport and the small deposit can be refunded when leaving the city.

The OP already has an Oyster card.

Consider downloading the Citymapper app for transit info in London. Every Londoner I know, and those here, use it.

Just wondering: Is taking the Tube tolerable? I know that sounds funny to some people. But for the last three years, I've taken the Heathrow Express. Someone recommended it to me b/c it was quicker, wasn't crowded and had air conditioning. Well, last year, the AC didn't seem to be working very well. For the sake of economy I'm considering the Tube. I do take it everywhere else while in London, so I'm thinking it'd be fine.

I would be arriving at Heathrow mid morning on a Sunday.

Thanks!

I take it everytime I fly into Heathrow. Easy to get seats and put your suitcase down. Never had any issues.

It really depends on where you are going. If you are staying near Paddington, then taking the Heathrow Express or TFL Rail is better than the tube. But for staying south of Hyde Park it would be a big mistake. You would save no time. Even for central or east London, the tube would probably be your best bet. And most cost efficient.

One last thing for those newcomers to London......on your return to Heathrow, not all Piccadilly line trains go to Heathrow. Make sure it says either "Heathrow 1,2,3 and 4" or "Heathrow 1,2,3 and 5"