will not lower

hi all sorry to come on and ask for help. i have a 2008 disco 3 it will not lower unless i go over 30. if i press tu
he up switch all is well however i then press to go down and it tries for a second then i get a fault on the dash.
i have programmed the key fob to do it it the hope it might be the switch no joy.
changed air drier
checked for air leaks (took about 3 weeks before i lost height in rear offside about 2cm)
compressor works fine.
cleaned all valve blocks.

please help i am now at a loss.
thanks Lindsey

Could possibly a height ride sensor???

i did think about that however my thinking was if it lowers while i am driving over 30 then the sensors must be ok.

i just had another go at her today. this time she tried to go down according to switch and there was a small hiss for a second or so then got suspension fault off road functions turned off. so i had another go and she went down a little then started to raise back to off road height