ideal combi esp1 35

Hi experts, I have a Ideal Logic Combi ESP1 35 boiler and its c.6 years old in my 'new' build. I also have a two wired Danfoss TP5000si thermostats, one upstairs and one downstairs connected to two Danfoss HPA2 2-port actuators, as you'd expect. Problem I have is that neither of the thermostats...