Hope someone can help me with details of how to get from Hilton Garden Inn T2-T3 to Terminal 3.

[Alaskanb]

Planning to stay at HGI T2-3 next April 8/9 as it's supposedly walkable to T3. As I have minor mobility issues I wonder if the walk is something I can do or am I better off staying on Bath Rd and taking a taxi who will drop me where I can access check-in for AA. Last week we had a dreadful experience with the wheelchair service at T-5 so hope to avoid that. Thanks. 

[Cotswold Eagle]

It is perfectly possible to walk, but the hotel is attached to T2. The official connection route is via the underground walkway that connects T2 and T3 with the various transport options, such as the station. This will be step free and pretty much level (from memory). I have no mobility issues and would expect to walk that in 10-15 minutes, if that helps. 
 

It should be possible to do it a ground level, but on the busy and confusing roads in  Heathrow Central, which are not primarily designed for pedestrian use. I would not recommend this. 
 

There is a hotel inside  T3, the Aerotel, which would be more convenient for you. 

[bobfrom jersey]

We stayed there recently and the walk was an easy 10 minutes and is the best way to get to the terminal as taxis are very expensive for the short journey. It is a nice hotel and the food in the top floor bar is particularly good. We would stay again if flying from either Terminal  2 or 3,

[Adlig]

Agree with previous comments. The Hilton garden Inn is a nice pre flight hotel. There is a You Tube video "Heathrow Airport Terminal 2 Walk to Terminal 3, Hilton Garden Inn Underground". Since you have mobility issues this may give you a feel for what the walk is like.The walk takes 10-15 minutes. The video was a little confusing at the end but you end up right at the lifts and escalator. There is also an interactive map on the Heathrow website. If I recall correctly the underground walkway is on level -1.