Hi,
I'm not sure if you have the same problem that I had (or yours might be a wiring issue?) but I've spoken with Ideal Heating, they have confirmed the old receiver was interfering with the Hive controls. The receiver needs to be removed and replaced with a Timer Link Plug. This will allow the boiler to only listen to the Hive calling for a demand. For me, I've ordered the timer link plug and will get my engineer to fit this on.
For the time being I left the old Ideal thermostat switched on at full temp and constant on. Seems to be a valid work around for the Hive.