Hi all... New member here... My name is Matt.  I have owned my 2003 X type for 5 years now... For me I love it. Been a Jaguar fan since 4 years old.  Wife bought me my first Jag for Christmas... 

However.... Having the habitual new tyre refits before the MOT, it was pointed out that the rear pads had gotten quite low and could be an issue for the MOT.  Having just spent a few quid on tires all round I'd just replace the pads myself.. (Not a difficult task) So, armed with new pads, set too and got them changed out.  All went swimmingly, and drove the car for the next few days without any issues. 
Did i mention I hadn't even touched the front brakes? Not even so much as removed the wheel.  But then out of the blue the front nearside brake is seized on! I use 1/4 tank of fuel and almost over heating the car Just inching her gently home.  Once the wheel had cooled enough, I had her back on the jack and inspecting the issue.... so tight was the brake I couldn't even turn the wheel with a huge great steel pole.  Sigh.  
So I set too, contemplating as to what it could be, asked some advice, as I hadn't even touched the brakes at the front.... Most of the advice came back as a seized caliper.  Great.  None of the other brakes were an issue.  Yeah I could've got one of those repair kits with new pistons etc... No... I just forked out and replaced ALL new discs AND calipers all round.  
All swapped out and YAY!!! She drove like a dream again..... 

For ONE !Removed! DAY! 
Same caliper seized on again.  
Now remember they're brand new! 
Brakes have been professionally bled with a continuous bleed system. 
So now I am stuck as to what it could be or were would be a good place to start looking for the fault and cause.  Only the font nearside is sticking... But, seems to release over night. 
I am able to drive the car but after a time the brake starts to lock on again.  
I get good firm braking, and the peddle isn't squashy in any way.  Engine doesn't struggle when braking.  

So, hopefully some collective minds maybe able to shed some light on what the issue maybe.  Or how I go about diagnosing the issue. 

Thank you in advance.

Wheelbearing overheating and seizing? 

Hi Manniewinaename... No it's not the Wheel bearing... it's definitely the brake seizing on.  I find it unlikely too as all the wheel bearings were replaced about 9 months ago. I now its possible one could go in a short time if poorly fitted, but find it unlikely as I say. 

Try changing the flexi hoses, sometimes they swell up on inside and do not release the pressure which keeps the caliper from releasing.

Funny you should mention that ... Someone else has suggested the same thing. Apparently the lining inside can fail acting like an aortic valve, stopping the fluid from flowing back, once the car is then left over night pressure in the lines can slowly decrease easing pressure on the caliper.   I have 2 new ones on order so fingers crossed. 

Either hoses or ABS issue (valve holding on that particular circuit/channel)

If the new hoses don't solve the issue, looking at the ABS unit will be my next port of call.... question though, would a sticking solenoid within the unit not throw up an error code or bring the ABS dash light on as a failure?  as I have neither engine management light or ABS light on. 

Ok so after months of trying to find out what the problem was..... It was indeed the ABS unit.  The front left brake channel had an issue whereby fluid was going in but a fault in the unit meant it would not let pressure return, thus locking the brake on.  3 mechanics came and went scratching their heads... 2 didn't even take payment from me as they couldn't solve or identify the problem... the other just went for an expensive global fix... "Brakes are shot mate... gonna need to replace the entire system!"....yeah right!

So it dawned on me that if I could do a test of some form Without disconnecting the ABS and throwing up fault codes etc.... So I simply disconnected the lines from the unit FL in and out, blanked them off then jumped the lines.... THE moment I disconnected the line from the channel...'PING' you could hear the caliper release. 
Ok so I conned the system. But it worked! Brake works perfectly, and so do the rest considering they're all still connected to the ABS unit.
Now I know this is NOT a fix.. but it did allow me to identify the problem.  And this is certainly NOT meant to be a get around.  But what is has shown is that the ABS unit was indeed faulty. 
This was then sent away to ECUTESTING.com who were brilliant.. They identified that a pin had become jammed shut, thus pressure could get passed but not return. 
They tested, overhauled, and recondition the unit, (looked new when it returned) for just under £200.. 
Now my cars a happy bunny again.