Zywall 110 - Wan answer ping

There a default firewall rule - WAN_to_Device, with a default allowed service group object - Default_Allow_WAN_To_ZyWALL.
You need to add PING into this service object group.

Here the steps,
1.On GUI, go to Object > Service > Service Group tab.
2.Click on Default_Allow_WAN_To_ZyWALL service group object.
3.On the left menu select PING, then click the Right Arrow, to put into the right menu. Click OK.