What is delayed start / optimum start? Optimum start or delayed start is a feature for the programmer. Normally you set the program times for when you want the heating to come on and turn off. With this feature you set the program times for when you want to be warm and the system decides when it needs to turn on. When the house is cold it turns on early but in mild weather it will switch the boiler on later because it doesn't take very long to warm the house up.

What is a load compensator/ weather compensator? A load compensator adjusts the radiator circulating temperature to be hotter when the house is cold. The weather compensator does the same depending on the weather (measured using an outside thermometer). This means you can run the radiators cooler when less heating is needed. This is a good thing because condensing boilers are more efficient at lower temperatures: ideally the water returning to the boiler should be no warmer than 55C.

What is the set back temperature? Some programmable thermostats have a set back temperature which is like a default or standby temperature - when the heating isn't "on", for example overnight, it will still maintain the house at this temperature.

What is a boiler interlock? This is the system which allows your thermostat and programmer to tell the boiler when to turn on and off.

What is frost protection mode? This is a minimum temperature which always applies, regardless of the other settings. This should be just enough to keep your pipes from freezing - around 5-7 C

What is holiday mode? Some programmers allow you to tell them when you are going on holiday and, more importantly, how long you will be away. When in holiday mode your programmer will keep track of the days and reset to normal before you return so you can come back to a warm house.

What are smart heating controls?Smart heating controls can mean a lot of different things. For example, load compensation is a smart control, especially if it 'learns' how long it takes your house to heat rather than asking you to select a temperature curve. Smart controls can also:

  • Turn the radiators off when the front door is open or windows are open
  • Turn the radiators down 1 or 2 degrees when there is no-one in a room
  • Prioritise flow through radiators where there is heat demand and adjust the radiator flow temperature when necessary
  • Give you remote control through your smart phone

There is a european standard for smart controls (EN 15232) which describes the services which can be provided and estimates the savings achievable in different situations. For a residential property with full automation the savings (over the reference case which is for a home with a condensing boiler, programmable thermostat with weather compensation and TRVs) are around 20%.

Why would I want a presence sensor? A presence sensor connected to your radiator valves can turn them down by 1 or 2 degrees when you aren't in the room - enough to save some energy but not enough that it can't warm up quickly when needed. If your house has a high thermal capacity it may take too long to warm up for this to be useful.