how to fix this...

[steveb21]

Gradually over the last few years a few tiles have popped off.

How would I fix/replace the tiles as I believe they come in a sheet?

How to fix the area under the coping?

What would cause this? I aim to keep CH at 400, although it has dropped to 200 at times.

Thank you

 

[RDspaguy]

Did you save the tiles that popped off? Put them back up and regrout. If you do not, you are unlikely to find that exact tile sheet, color, and pattern. Patch it up and deal with it, or get new tile.
As for the cause, could be a number of things. Low ch, low ph, moisture penetration from cracked tile or coping grout, high water level in winter, salt crystalization, poor installation, cheap materials, cracking concrete behind the tiles, etc...

 

[steveb21]

Kept most of them - not all though!

Any special grouting material required? First time i will be doing this

 

[RDspaguy]

Try to pop more tiles. Hammer them with your hand, push on corners. Might as well get any that are loose but haven't fallen off yet. Wouldn't hurt to scrape the grout and redo it, but that is a tedious job with 1" tiles. Trust me, I know.
Clean out the old thinset with a chisel or screwdriver. Reset tiles with thinset or epoxy. Allow to set. Grout as usual, the better the grout, the longer it will last. Tuckpoint or mastic the coping.

 

[steveb21]

Thanks.

Would epoxy work to stick the tiles back on and also fill in the other gapes underneath the coping area?

On the patio area around the pool the pointing within the slabs has cracked on many places (old picture below) what is best to fill this with? I believe the previous owners used material which was non expanding - hence why the cracks have appeared. Highlights the area's in red.

 

[RDspaguy]

Mastic. Google "pool deck caulking" for videos.
Epoxy will discolor over time, and is next to impossible to remove. You could not apply it like grout, you would have to run each joint and it would be a huge mess. I would not recommend it.