Tektro Auriga Pro brakes - how to service

This is my first post and I hope someone can help. I've been riding bikes for 30 plus years and in that time had very many different bikes. About a year ago I got a new commuter bike (landrover commute 6.9) following being wiped out on my Dawes Sonoran at a roundabout by a police officer. The landrover was cheap and funds were tight and on the whole it has been a good buy. My only problem is the Tektro hydraulic brakes. About a month ago the rear brake just seemed to stop working. The brake lever has gone from being taut to pull to pulling right back to the handle bars just by pulling with one finger. I have checked the manual for the brakes and it is no help. I've searched the internet for ideas as to what the fault is and I thought it might be that they needed bleeding. So i purchased the bleed kit and followed tektro's instructions to no avail. I tried bleeding it at the caliper and from the lever to no effect. Anyone any advice or am I best just putting it into my local bike shop ?