Heating Controls – Smart or Not-So-Smart

I install heating controls, including “smart” controls, and feel I have a reasonable working knowledge of the subject which I shall attempt to share with you in this brief non-technical summary article, along with some views.

I’ll start with the simplest system and progress to the most sophisticated.

All heating control systems have in common that they regulate the heat source (boiler), turning off or reducing its power, avoiding overheating and reducing energy use and cost. They don’t make your property any warmer.


Timer (programmer) + manual radiator valves:

The most basic system only has a time control, no room thermostat and manual radiator valves (in contrast to thermostatic radiator valves or TRVs).

The only thermostat is on the boiler, and I shall dwell on this because all systems share this feature; a control on the boiler that controls the temperature of the water leaving the boiler (the “flow” temperature) and thus the radiator temperature.

People are often perplexed where to set this control, not helped by the fact that on many boilers there is no indicated temperature (some modern boilers display temperature).

If you have stored hot water (a cylinder), the aim is to heat the water in the cylinder to 60 celsius or more to kill Legionella bugs, so the flow temperature from the boiler should be 65 to 70. This makes for hot radiators, hotter than need be, but that’s the deal, unless yours is a relatively rare and sophisticated boiler that incorporates the heating controls and separately controls stored hot water and radiator temperature.

If you have a condensing combi boiler (probably fitted after April 2005) and no stored hot water, you have the luxury of setting the radiator temperature separately from the hot water, in which case, turn down the boiler thermostat and run the radiators as cool as is compatible with comfort. This will help the boiler to condense, making it more efficient and saving you gas and money.

Back to the radiators: without TRVs the only way you can control temperature in the rooms is to go round adjusting the manual valves. You are pretty much doomed either to be too cold or to waste gas.

Such a basic system is now fairly uncommon.


Timer + room thermostat, with manual radiator valves:

This system is not uncommon. A room thermostat, frequently placed in a hallway, adds a measure of temperature control to the system, essentially preventing the place overheating.

Control of individual room comfort still relies of manual adjustment of radiator valves.


Timer + thermostatic radiator valves (TRVs), with no room thermostat:

This is also not uncommon and is the system I had for thirty-seven years. TRVs add a measure of thermostatic control to each room, greatly reducing the need to go round making adjustments. However, there is no overall control of temperature so for example, to run the property cooler in periods of absence requires doing the rounds to turn down the TRVs. In my case the system is small so this wasn’t too onerous. The TRVs are effective in reducing energy use.


Timer + thermostatic radiator valves (TRVs) + room thermostat:

Now we’re talking! Standards for buildings are enshrined in law by the Building Regulations, and Part L deals with energy conservation. The government publishes a compliance guide on how to meet the regulations:


Section 3.0 covers “Control of space heating” and reference to it will show that this system complies.

Classic work done at Salford University in their huge environmental chamber and published in 2013, showed that energy savings of up to 40% were possible by adding TRVs and a room thermostat, a far bigger figure than I or many others would have guessed (I’d have guessed 10%):



Wireless room thermostats

Not that many years ago, fitting a room thermostat involved not only mounting the thermostat unit on the wall, but running a cable from the thermostat back to the boiler controls, which could be messy and disruptive as the cable run could be long.

Thanks to modern wireless technology, a battery-powered thermostat unit communicates with a receiver unit located with the boiler controls, requiring only a short length of cable and making installation much easier and less expensive. The thermostat doesn’t even have to be fixed to a wall – mine sits on a horizontal surface such as a shelf. It can be taken into a room where control is particularly desired, the TRV turned up full, and the temperature set for comfort.

My wife teaches in the sitting room, and placing the wireless thermostat there means that that room is at a suitable temperature.

Another example of the flexibility afforded by a wireless thermostat is controlling the temperature in a room where someone is ill, or ensuring that an otherwise cold bedroom reaches an acceptable temperature on a cold winter’s night.


Adding weather compensation:

All the controls mentioned so far essentially end up giving a switch instruction to the boiler, amounting to “demand for heat”/”no demand for heat”, and the boiler sorts out whether to burn gas or not according to the temperature of the circulating water.

Modern boilers so designed allow the flow temperature to be externally controlled. An external temperature sensor is connected to the boiler. When it’s cold outside the boiler increases the flow temperature so the radiators run hotter for a quick warm-up time, and conversely when the outside temperature increases.

This makes perfect sense in keeping the circulating water temperature, averaged over the year, lower than without weather compensation, helping the boiler to condense more, saving energy. As the difference in gas consumption between condensing and non-condensing is typically 6%, I’d expect weather compensation to save a fraction of 6% – not particularly exciting.


Smart controls:

A great deal of technical development and marketing activity has taken place in recent years in the field of boiler controls, and “smart” controls in particular. This may in part due to boilers having achieved efficiencies that are unlikely to see much improvement, so efficiency gains have to be found elsewhere. These are underwritten by the EU Energy Related Products (ErP) Directive in which systems are awarded brownie points according to energy saving measures installed, which includes heating controls.

What do we mean by a smart control? Perhaps it helps to look first at controls which aren’t smart. Take my programmer and wireless room thermostat. I set the programmer to deliver heating and hot water at certain times of the day, and the room thermostat is set for a suitable temperature. If no-one’s at home, the system operates in the same way regardless, and there’s nothing I can do about it while I’m out.

Smart controls could allow me to set times and temperatures through my smartphone (if I had one) or the internet. They could keep track of my position and turn up the heating as I approach home, and turn it down as I head away. The could learn my pattern of movements and adjust the heating in anticipation of my arrivals and departures.

From an installation (wiring) point of view, there’s little added complication over standard heating controls – ultimately, it comes down to a switch that signals a demand for heat, which means connecting a receiver unit near boiler or heating controls.

The user interface on a number of smart controls is extremely impressive – virtually a work of art.

It’s a technological marvel so we should all have smart controls – shouldn’t we? Judging from the marketing of smart controls, their advent ranks in importance somewhere between the printing press and the wheel (you may be detecting a hint of scepticism).

Here are some of my reservations:

  • Heating controls have traditionally had a long life, whereas mobile phones tend to be replaced every few years, so I’m unsure as to the likely lifespan of smart controls. My original system installed in 1978 had a Randall timer. Umpteen years later it failed but I was delighted to find it was still available – it still is! (It’s now labelled Danfoss who acquired Randall.)

  • Nest in particular, with its beautiful user interface, uses wireless communication but requires to be powered via wires. While that means it conveniently replaces a wired thermostat, it loses some of the potential benefit of freedom of a wireless device.
  • Some smart controls learn the household pattern of behaviour and adjust the heating accordingly. That’s fine if there is a regular pattern, but if not, there’s nothing to learn and the advantage is lost.
  • One smart system I came across didn’t recover from the power being off while the boiler was serviced and had to be manually reset. So if there is a power cut while you’re away, you’ll come back to a cold house – granted that’s fine for saving energy but not so smart if your house freezes.
  • Will internet-based heating controls be hacked?

I’m not trying to put you off smart controls, merely to point out that nothing is perfect and there always trade-offs. Do be sceptical about the energy savings claims as they are very difficult to verify.

My advice is to take time to think carefully about what you want heating controls to do for YOU, and how YOU want to operate them. Take time to study some reviews, such as this one:


If you see a product and instantly want one, that’s exactly what the marketing people seek to achieve – stop, think and take your time.


Appendix – my heating controls


Programmer: Drayton LP722

Wireless room thermostat: Siemens RDH10RF