aqualisa quarts ?

can anyone help me please,do not answer if a guess or your idea because ive tried it,facts please. we had a new boiler fitted and seems like since that,my aqualisa shower will not stay on hot,if you select cold it seems to be ok until you try to increase the heat ,then it just stops,if you start on hot you,ll get 3 maybe 10 seconds then cuts out,the girl from aqualisa told me to change the front control which i did £60 no fix then she told me to change the wire £25 no fix,it seems like the heat sensor aint working any ideas? i know from reading the blogs alan had the same problem but no answers please help