morphy richards jet steam elite - steam is intermittant?

This iron is rarely used and has a non-original filter fitted.

When I switch it on & select steam it can work for a few mins & then the steam function stops. It can start to work again after a few hours or sometimes I have to keep trying for days.

I know the reservoir float is working as it should.

Is there any material difference in an original and a non-original filter which might be the problem? I don't want to buy a new original filter only to find the same problem.

We live in a low lime scale problem area.