Sprinkler question, rotor not turning until I reduce pressure.

[alkemyst]

I will probably just buy another one (K2 Smartset by K-Rain), the filter looked fine but I flushed it anyway.

The sprinkler will pop up but not turn until I reduce the pressure slightly and restore it. Sometimes it works fine without doing this.

Is there anything I can 'clean'? The manual doesn't say anything other than the filter as serviceable.

Thanks