I was riding the other day when suddenly I lost all front brake pressure on the lever, then the calliper started to drag causing the disc to cook! I drained fluid and re bled system and thought the problem was solved but yet again about 30 mins into ride the front brake lever lost all compression and the brake started to bind. As previous when disc seems to cool ( and calliper) the pressure comes back but I'm far from happy as this brake failure happened while I was travelling on a road section!! Very odd how brakes ( front only) will be fine then loose them completely then once cooled ( heat generated from binding) the lever pressure returns. I will now have to replace all seals in calipers as probably ruined due to excess heat. It's not as if they are being subject to hard use as usually failing when trialing.

Many thanks
Dan

Usually happens when not enough play is left for the piston. Too tight on both adjusters.

Try taking the caliper off, removing the pads and give all around the pistons and inside where the pads sit a really good clean. I have had the same issue several times and found that cleaning the inside sorts it out. Think it is because mud goes hard and sets around the pistons/seals and then when the bike is used again the hard mud won't let the piston return causing the brake pads to bind causing the extreme heat. I now carry a 5 litre bottle of water in the van so if I happens I pour some water over the disc etc and it usually sorts it out so I can finish the trial and get home and then give it all a real good clean

Adjustment may be the issue too. If the brakes are binding just a little they will overheat and bind fairly quickly even in light usage. I would check all adjustments. On the AJP master you need to make sure there is a small amount of free play in the lever before it engages. The adjuster actuating the piston should not be in contact with the piston before you depress it. The other adjuster controls the distance the lever throws from the bar. This also needs to have clearance to allow for free play. Failing this, pull it apart again.