Thor, or should that be Zeus?

[Chaz]

I have known the spindle fittings to be blocked when they seal the top bit on. Take off the tubing and poke a small screw driver down the hole to see if it is restricted about 25mm down. I only use a 2 ltr tank and a very small fish tank pump around £3

Thanks. I did think of that - I tried to blow into it but a bit limited in terms of space. The black grommit things were removed, wasnt sure if there could be anything else blocking.