Hi @FE7,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
When pop-up sprinklers don't retract, it is often because dirt has gotten into the mechanism. I'd suggest you pop out the heads and flush them with clean water to remove any dirt or debris.
An application of a silicone-based lubricant, such as this Boston Aerosol Silicone Spray would also certainly be worthwhile.
Give this a try and let me know how you go. I am happy to assist further if required.
Jacob
