I want my neoStat to switch the heating on when the temperature drops 0.5C below my set temperature

neoStat v1 (Blue display light)

You need to adjust the "switching differential" in your thermostat. To do this, follow these steps;

• Navigate to Setup and press tick
• Use the Up arrow until the small number (top right) is 02.
• Press Tick
• Use the left arrow select 00.5
• Press tick

neoStat v2 (White display light)

You need to adjust the "switching differential" in your thermostat. To do this, follow these steps;

• Navigate to POWER icon and hold the tick until the temperature in the centre disappears. 
• Select Setup and press Tick
• Use the Up arrow until the small number (top right) is 02.
• Press Tick
• Use the left arrow select 00.5
• Press tick