[Familyman 90]

Disconnect the pipes from the jets and give it a squirt. If you see a good flow then the jets may be a big grunged.

You can potentially blow them through with an airline, soak them in cleaner, use pins, etc, but new ones aren't expensive if required.

To prevent a recurrence use a decent strength screen wash mix, not too dilute, and give them a quick squirt every couple of weeks whether required or not.