Neptune shower not working?

I have a Neptune shower that was working perfectly until taking it off to tile behind it.
Since re fitting exactly the same as it come off I switched on and it hardly had any pressure and got really hot.
I removed it again and cleaned the little filter on the inlet but this made no difference.
All it does now when you switch it on is no pressure and doesn't get hot.
I have good water mains to it and it also doesn't stop water coming out when switched off.
Please advise what could have changed since removing it.
The filter was thick with tile dust etc but I have since cleaned it and still no joy. It's like it isn't getting enough water but it definately is.
Thanks Shaun