erc-server-send-ping-timeout

erc-server-send-ping-timeout is a variable defined in `erc-backend.el'.
Its value is

120

Documentation:
If the time between ping and response is greater than this, reconnect.
The time is in seconds.

This must be greater than or equal to the value for
`erc-server-send-ping-interval'.

If this is set to nil, never try to reconnect.

You can customize this variable.