Because there is minimal configuration overhead (from an Office Web Apps perspective) and zero data loss, there is little risk to rebuilding a farm. These steps can be a legitimate part of an action plan for resolving technical issues with Office Web Apps.
1. Take farm offline (if there is a load balancer)
2. Powershell: Get-OfficeWebAppsFarm > c:\MyWACfarm.txt
3. (If multi-server farm) Remove each child machine from the farm using Remove-OfficeWebAppsMachine, then on the parent machine run the previous command. This will delete the farm.
4. Reboot the Office Web Apps server(s).
5. New-OfficeWebAppsFarm using (if appropriate) parameter values from "MyWACfarm.txt". Below is an example and screenshot (you will want to refer to the settings from your "MyWACFarm.txt"):
New-OfficeWebAppsFarm -InternalURL "http://<WacServer>" -AllowHttp -EditingEnabled -OpenFromURLEnabled
6. Reunite the children with their parent! Run this from each child server:
New-OfficeWebAppsMachine -machinetojoin <ParentServer>
Note: <ParentServer> is not present in above screenshot.
7. Bring farm back online.
Note: You may want to rebuild the bindings (On SharePoint Server > Powershell):
Remove-SPWOPIBinding –All:$true
New-SPWOPIBinding –ServerName “Server.corp.Contoso.com” -AllowHttp
Useful Resource:
Configure Office Web Apps for SharePoint 2013
http://technet.microsoft.com/en-us/library/ff431687