Started with the yellow light and chime, codes C1A20 Pressure increases too slowly- signal plausibility failure and C1A13 Pressure does not decrease when venting- signal plausibility failure.
I have refurbed the compressor with new seals and relief valves, and dryer, stripped and changed o rings in all 3 valve blocks, checked for blocked silencer but still got the C1A13 fault.
I have also done a continuity check on the exhaust valve wiring back to the control module but didn`t think to load test.
Any help appreciated and recommendations for a garage near Coventry

When replacing Orings, where did you get them? Who was supplier (not eBay).
When you leave the car overnight with suspension fuses removed, do you get any change in height at any corner? Take measurements before and after an 8 hour period.
What pressure does gallery charge to and what pressure is gallery after 8 hours (check this after 8 hours without turning car on) then turn car on while reading live data and verify what it changes to (as middle valve block activates), take pressure reading and verify if compressor kicks in, if it does does it take long to pressurise system?
Does car respond to change in height in adequate time and without other issues?
Also, can you grab a diagram and just verify your connections to valve blocks are right way round, this is worth the effort just in case a simple mistake ( I checked this twice on mine to be sure!).
If you can get this info, I might be able to help. That code for pressure does not decrease when venting was orings in valve blocks for me, and was a residual issue after I put in the first set of orings which were crap. Rather than assuming these are still your problem, if you can check all of above we may be able to work through it. Also, check out the pdf file uploaded on my issues and resolutions for the air suspension. Added in the faults and fixes section today.