My mk2.5 titanium estate is having trouble with its boot. It unlocks fine with the remote key but the keyless entry has stopped. 

By "keyless" I presume you mean the rubber-covered button under the tailgate trim. If so it's fairly common for water to find its way into these and cause corrosion.

The button is only used for locking the car via the keyless system, it shouldn’t affect opening the boot if you’ve got the fob close too it. 
 

Know this as mines failed as well but I can still open the boot if the car is locked.
 

Could be a problem with the sensor for the keyless system or the wiring to it - on the hatchback the sensor lives on the middle of the chassis beam behind the bumper, if the estate is the same you can look at it if you jack the back of the car up and get underneath to see if all looks ok

3 hours ago, troy45 said:

The button is only used for locking the car via the keyless system, it shouldn’t affect opening the boot if you’ve got the fob close too it. 
 

Know this as mines failed as well but I can still open the boot if the car is locked.
 

Just to avoid any confusion, you're talking about the button on the door handle and not the one that mjt is talking about (just above the rear number plate).

I’m talking about the small black button on the tailgate finisher, not the boot release button underneath. 
 

Reading the OP again now I’ve got the buttons mixed up 😳 if the underside release button fails then yes that’ll look like keyless entry has failed and yes to mjt’s post as well that those are prone to getting water in them. 
 

Hopefully a lot easier to fix than trying to diagnose issues with the keyless sensor, I think spare buttons are available either through Ford or EBay/Ali express etc

You could prove it out by unlocking the car first then trying to open the boot on the button?

Thanks for the input guys. The little square rubber button has never been functional on my car. (Not sure what it does really?)

Im going to have a look under the car for the possible dodgy sensor. Cheers

16 hours ago, Southcoastfocus said:

Thanks for the input guys. The little square rubber button has never been functional on my car. (Not sure what it does really?)

Im going to have a look under the car for the possible dodgy sensor. Cheers

I have Keyless entry on my MK2.5 Focus. The little rubber button locks the car just like the buttons on the driver and passenger door I believe, if my car is locked that button won't do anything.

Brilliant. Cheers. 4 years I’ve had the car and now I know. 🤣