The service “httpd” appears to be down.
OK just to give an update on this thread, so hopefully it helps someone else in the future.
Apologies in advance to any Level 18 Fire Breathing +5 SysAdmins; this is noob stuff
The cPanel team examined my server and determined that Apache had ran out of Semaphores.
Each time HTTPD crashed it didn’t release the semaphores and eventually my server ran out (I had 128). The cPanel team kindly cleared down the “locked” semaphores as follows: