How to change ssl certificate for a site with HSTS enabled?

Hello. Not so long ago under my wing moved the site with the expiring certificate. Instead of re-issuing of the certificate from the old certification authority, I decided to try out Let's encrypt. Works. But. On the old site was included HSTS. I pointed out need a sha256 sum and everything seems fine. BUT. Began to receive complaints that the site is not available. Error in Firefox: MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE. In Chrome the same. The problem is not unique. keep-alive for the old certificate was set equal to the year.
What you can do in this situation? To return to the old service provider is clear. But how then to change the certification authority, if the need arises?
Disabling HSTS doesn't help.
July 9th 19 at 13:32
1 answer
July 9th 19 at 13:34
Thanks for the reply and sorry for the confusion with the terminology.
You write: can not cope. Not to cope at all? Even through the purchase of the certificate from the previous certification authority?
There in the header was specified no single sha256, but several. This is probably the thumbprints of the certificates that are higher in the chain. That is, the certificates of certification authority. In this case, if these certificates have not changed, the error will disappear, right?

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