firewall port block enable ssh

Hi everybody ! Im trying to use iptables to block all ports but one for a specific IP on my lan. But I have no luck :( Router : RT-N66U@MERLIN / 192.168.0.1 Device/IP : 192.168.0.133 The IP belongs to a central heating unit which runs a VNC server (@5900),and is able to be controlled via an...