Unscheduled host checks

I am running Nagios Version 3.0.6 on Solaris 10 update 6.
If I define a host with these options:

check_command check-host-alive
active_checks_enabled 1
max_check_attempts 3
check_interval 1440 ; Sigh, check the hosts daily
event_handler_enabled 0 ; Host event handler is enabled
flap_detection_enabled 1 ; Flap detection is enabled
failure_prediction_enabled 1 ; Failure prediction is enabled
process_perf_data 0 ; Process performance data
retain_status_information 1 ; Retain status information across program restarts
retain_nonstatus_information 1 ; Retain non-status information across program restarts
passive_checks_enabled 1
obsess_over_host 0
check_freshness 0
contact_groups Primary_contacts
notifications_enabled 1 ; Host notifications are enabled
notification_interval 20
notification_period 24x7
notification_options d,u,r,f ;down,unreachable,recovery,flapping

Then the host gets pinged daily as expected.
However if I remove the “check_interval” the host gets pinged every 5 minutes.
The behavior is supposed to be no host checking if no "check_interval"
What is causing these checks to get scheduled, and how can I stop it?

Thanks very much for any help

Do you use any host templates which could have check_interval and check_command variable defined?