After configuring a new headless Raspberry Pi Zero W *and* headless Raspberry Pi 3B+ with the full version of Raspian, I have not been able to ssh into it over WiFi. The IP address is assigned and pingable, but I get 'connection refused' errors when tryin to ssh into them.

After some research, I discovered one possible solution is to replace the SSH host keys on the pi.

But it's a Catch-22, because I can't login to the pi to change the keys that I need to change to be able to log into the pi. 

What can I do?

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***Background detail:*** The way I configured my Pi's are as follows: Using __Etcher.app__ on __macOS__, I flashed an SSD card with the ___full___ desktop version of Raspian, `2018-11-13-raspbian-stretch-full.img`, downloaded from the Raspian site, and installed it on a __Pi Zero W__ and a __Pi 3B+__, both headless, and used the *headless* approach to configuring WiFi and ssh (i.e. touched `ssh` in /boot and created `wpa_supplicant.conf` in /boot).  

I didn't have this problem when I similarly installed Raspian ___lite___ (on my Pi 3B, about a month ago, `2018-10-09-raspbian-stretch-lite.img` 

At the moment I'm wondering if possibly installing the full Raspian on a headless Pi may thwart OpenSSH configuration (e.g. requires raspi-config to be run by user or something).


*I will update this question if I find out the root cause to this, and whether the workaround is the best answer*

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_Follow-up to @Milliway's comment below_: This is the Reddit thread containing post that gave me the idea that regenerating host keys might fix the problem:

https://www.reddit.com/r/raspberry_pi/comments/704v5y/ssh_connection_refused_off_a_headless_setup/