Just in case anyone else ends up in the same place as me..............
I managed to solve the issue and found there was no access to the internet on the PRINTERS VLAN, despite having the firewall rules allowing it!
Eventually I stumbled upon the Firewall NAT Outbound rules, which was populated with 2 rules per VLAN (had been done automatically, presumably when setting up the VLANs).
These rules did not exist for the PRINTERS VLAN. Added these rules manually and all sprung into life!
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What I cannot understand is why these had not been created in the first place!! The outbound NAT mode was showing 'manual outbound NAT rule generation'.
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Thought this would have been set to Auto??
Never mind, all working now but at least I've picked up some extra knowledge. Thanks to everyone for helping me sort this out, it is greatly appreciated.
Steve