Heatmiser deals with the control side of the heating, not the manifold and plumbing side. When the thermostat calls for heat, you will see the flame icon. If the Heatmiser Wiring Centre responds, you will see zone lights responding. The boiler enable should come on. That means that the control side is working fine.
Therefore as long as the controls are on, it will suggest an issue with the water based underfloor heating, not the controls, which can usually be resolved by a heating engineer or a local plumber.
If it is electric underfloor heating, it would be a case of getting an electrician to investigate.
Please note that when it comes to any room heating, a room is only going to warm if there is sufficient heat to bring the room up to temperature. Therefore the temperature of the water in the floor is not hot enough, or the room loses heat due to draughts and insulation issues, the room may not get sufficiently warm enough which is out of Heatmiser's control.