Water hammering since swapping controller

Since swapping the Honeywell controller and thermostat to Tado controller and wireless thermostat my heating has started to bang. Whenever the controller commands the heating on or off we get a loud bang through the pipes. Haven’t isolated any particular location yet. I’m guessing the timing of the boiler/pump/valve switching has changed when we swapped the controller and that’s why it started.
I’ve checked for air in the heating system, there’s none. It’s gravity fed from a header tank in the loft so pressure hasn’t changed. There are conventional TRVs on all radiators, no Tado TRVs (yet).
Any ideas?