503 Server Error: Service Unavailable for url:” means the web server (or an intermediate device, such as a reverse proxy) is not behaving itself. See: https://httpstatuses.com/503
This is not caused by any deficiency in the custom component - the Honeywell servers are well-known to be relatively unreliable.
As an aside, this is such a common scenario (where the component code is blamed for an unreliable Honeywell web server) that I managed to convince the author of the client library (evohomeclient) to add the functionality to report HTML status error codes (i.e. anything other than 200, SUCCESS).
This custom component is using my fork of that (new) client library (FYI: the existing Honeywell component uses an ‘older’ version of evohomeclient, that does not report HTML status return codes - and v1 of the api only).
Failed to increase precision of temperatures via the v1 api. Continuing with v2 temps.” Almost certainly related to the above issue, but happy to investigate if not - come back to me when that error appears by itself.
Background: higher precision temps will be displayed as (say) 26.7 (PRECISION_TENTHS) instead of 26.5 (PRECISION_HALVES), although they are stored internally to the nearest 100th.