What each number means.
ERROR 520: unexpected response from the origin. Usually our server returned something malformed, or the connection dropped. Check our error log.
ERROR 521: the origin refused the connection. Our server is down, or something is blocking Cloudflare.
ERROR 522: connection timed out reaching the origin. Our server did not respond in time, frequently resource exhaustion.
ERROR 523: origin unreachable. Usually a DNS misconfiguration; the record points somewhere wrong.
ERROR 524: the origin took too long to respond. Your application exceeded the timeout, which is a slow page rather than a Cloudflare fault.
ERROR 525: SSL handshake failed between Cloudflare and us.
ERROR 526: our certificate is invalid, with Full (strict) set.
ERROR 1020: a firewall rule blocked the request.
WHAT THEY HAVE IN COMMON
Errors in the 52x range mean Cloudflare could not get a good response from us.
Check cPanel > Metrics > Errors and Resource Usage at the same time.
WHAT TO SEND US
The error number, the time, and the URL. The number narrows the cause considerably.
