Getting from Heathrow terminal 3 to 5

Is this the site you used? https://www.heathrow.com/connecting-flights

Are the flights a single booking?

Checked luggage?

There is no guarantee that you will be landing or departing from those gates. All you can be sure of is landing at Terminal 3 and leaving from Terminal 5. Contactless payment does include ApplePay. See below

Others may confirm my feeling that as you will be travelling on the land side transport service, you’ll have to go through immigration in Terminal 3 and go then through security in Terminal 5. If you’re travelling on one ticket your luggage should go straight through to Edinburgh; if not, you’ll have to collect it before you leave Terminal 3 and re-check it in Terminal 5.

From the Heathrow website:
“ Free London Underground services and shuttle trains (Elizabeth Line and Heathrow Express) are available for inter-terminal transfers between Heathrow Terminals 2&3 and Heathrow Terminal 5.
Please note that a Transport for London Oyster card or contactless payment mechanism is required to activate the ticket gates on London Underground services, but you won’t be charged for your journey as long as you only travel between terminals.
If you are using Heathrow Express or Elizabeth Line, please obtain a free inter-terminal transfer ticket from one of the machines in the station for your journey.
Average journey time: 20 minutes”

We have used Heathrow Connect, the link Joe42F listed above. It has made the transfers easy with no surprises. I wish all large airports offered a link that that.

Thanks for all the responses. I used the link Joe sent, had not seen that, and it confirmed the arrival at terminal 3 and departure again from Terminal 5 with a transfer time of 90 minutes. Wow, that's a long time, about as long as the flight to Edinburgh! Can anyone confirm it really takes this long? Thanks Joe for the link. Glad I looked for a flight with a long layover. We did book all the flights together so should have to retrieve luggage.
Amanda that is the information I saw at the Heathrow site so I'm assuming that is the plan we will follow to get from one terminal to the other. We will pick up a ticket and use our phones at the gate.
My next question is there signage for the Heathrow Express or do we follow the purple signage to get us around?

The 90 minute minimum connection time (when traveling on a single ticket) is supposed to allow reasonable time to deplane, take the bus between terminals, go through passport control, get a boarding pass for your connecting flight, if necessary, go through UK security, and get to your connecting gate. In other words, having at least 90 minutes "guarantees" you can do this.

If you're on a single ticket, you will follow the purple signs to the buses, which will take you directly to T5.

If you are not on the same ticket, you will have to go through immigration in T3, retrieve your bag, pass through customs, then go down a well-signed ramp to the Heathrow Express platform. They were working on the ramp last time I went through, so I'm not sure if that's changed. Anyway, once in T5, you will then check in, check your bag, go through security, and eventually go to your gate.

We have done that transfer a few times, most recently June, 2022. The Heathrow Express runs about every twenty minutes from T3 to T5. You have to get a ticket, but the ticket is free. It is a LONG walk from your landing gate in T3 to the HEX station and another LONG walk from the HEX station in T5 to your departure gate. Wear comfortable shoes.

You are getting confusing information some of which is wrong.

Jeff, once again, we have to know.......is this on one ticket or did you buy the two tickets separately?

If you bought them together.....then follow the instructions on the flight connections website. When you get off the plane, you will folllow the flight connections signs. Eventually there will be two signs--one for people staying in the UK (you) and those who are not. Follow the staying in the UK signs. You will go through immigration (not the main immigration hall but a smaller immigration area for connecting passengers.) Then through security. You then board a bus (airside) that will take you to T3. The bus is free. At T3, go to your gate. If you have any checked luggage it should be checked through to Edinburgh.

If these are two tickets, then you will have go to through regular immigration, make your way to T3 by Heathrow Express (no charge) and at T3 you go thorugh security and then to your gate. If you have checked luggage you will have to retrieve it at T5 and take it to T3 to check in. (However, if you only have carry on luggage, I would try to do the Flight Conncections transfer first rather than the hassle of going between terminals on your own. They might let you especially if you already have your boarding pass for your next flight.

Gates are assigned daily so a gate the plane operates out of today may be different tomorrow. (Most domestic flights are out of T5A not B. But don't worry about that. You won't know until you arrive at T5.)

The 90 minutes posted is the minimum time they suggest for the transfer. It probably won't take that long.

Providing you do not need to retrieve checked bags you can use the Flight Connections route for immigration even on separate tickets. You will always go through security changing at a British airport from overseas as the UK authorities do not trust the competence of any other country.

OK, I think this is making sense to me now. We are on one ticket (AA from USA to UK then BA to Edinburgh) so we will follow the purple connection signs to take the bus from terminal 3 to 5. Then it looks like we will be able to use the e-passport entrance to pass through immigration to the UK. Once in terminal 5 if our gate is in 5A or 5B we would take the tram to those and then find our gate.
If we were on separate tickets then we would have to leave security, go through main immigration and then find the HEX train station to get to terminal 5. I can see how that would take 90 minutes, hopefully it won’t take us that long.
Thanks to everyone for your help, and especially to Frank for clearing this up.

No.....you land at Terminal 3, You will go through immigration there and you should be able to use the passport gates. You will then get on the bus for Terminal 5. (I don't remember if you go through security at T3 or T5. Don't worry, you will be told.)

You will arrive at T5. The main terminal are the A gates. You only have to take the tram to either saterllite terminals 5B or 5C.

Since it's on one ticket forget about what you have to do if it was separate tickets.

Seriously, relax. There are signs everywhere. There are people there who can answer your questions. It's not as difficult as you are making it.

Yeah, I did this once, and didn't give it any thought. Just followed the signs and ended up where I was supposed to go with time to spare. But the airport is just humungous, so look for the signs.