HT BUS is a digital interface that actually works in low voltage. While 230 V would be what relays work with. If 230 V has been connected to the low voltage terminals in the tado device, this could've been damaged.
Normally the BUS interface is better, as it allows a modulating control of the boiler, which is more efficient.
If you may, I'd suggest you to contact our support with the details of your installation (and pictures of the wirings) so we can help you figuring out how has it been done