Safety first: No wiring changes required.

Steps:

In the installer menu, set the control type to TPI (Time Proportional Integral) or similar advanced mode recommended by Heatmiser for your system.
Adjust the cycle rate or proportional band according to the heat emitter type (radiators vs. underfloor heating).
Ensure the thermostat is mounted on an internal wall away from direct heat sources and draughts.
For underfloor heating, enable any floor limit and preheat/anticipation settings recommended by Heatmiser to reduce overshoot.

Thermostat frequently overshoots set temperature, room gets too hot

Possible Causes