The following IP ranges need allowed through your firewall on the port you have specified in the health check:

{
"ip_prefix": "54.183.255.128/26",
"region": "us-west-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.228.16.0/26",
"region": "eu-west-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.232.40.64/26",
"region": "sa-east-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.241.32.64/26",
"region": "us-west-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.243.31.192/26",
"region": "us-east-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.244.52.192/26",
"region": "us-west-2",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.245.168.0/26",
"region": "us-west-2",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.248.220.0/26",
"region": "ap-northeast-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.250.253.192/26",
"region": "ap-northeast-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.251.31.128/26",
"region": "ap-southeast-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.252.79.128/26",
"region": "ap-southeast-2",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.252.254.192/26",
"region": "ap-southeast-2",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "54.255.254.192/26",
"region": "ap-southeast-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "107.23.255.0/26",
"region": "us-east-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "176.34.159.192/26",
"region": "eu-west-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{
"ip_prefix": "177.71.207.128/26",
"region": "sa-east-1",
"service": "ROUTE53_HEALTHCHECKS"
},
{

Official IP Ranges from AWS – https://ip-ranges.amazonaws.com/ip-ranges.json