VRRP seems to be broken

I have two PC RouterOS routers, (6.13) with an IPv4 VRRP interface facing my firewall. From either router I can ping the real and virtual IP addresses of the routers but from the firewall I can only ping the real addresses on the routers, the virtual does not respond. All aspects of the VRRP setup appear to be correct. I have run out of ideas with respect to what to look for. Any clues would be appreciated.

Whilst my troubleshooting is using ICMP, I can not route any IP traffic via the virtual IP, which was the whole point of using VRRP. My temporary workaround has been to route to the real address of one of the routers but the breaks my redundancy.