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Modernising your heating controls and improving boiler efficiency

Fancy knocking some money off your gas bill? Which? Trusted Trader Alec Morrow explains how to improve or update your heating controls to get the most for your money.

In this article

Out-of-date heating controls could be costing you money. Most boilers in the UK use a binary ‘on/off’ control, which either pumps out the full force of the boiler, or nothing at all.  Although this system has become much more efficient in recent years, it still wastes significant amounts of energy.

Which? Trusted trader Alec Morrow, of Integrated Heating LTD, recommends installing a modulating room controller. This regulates the temperature in your home, reduces the fluctuations you find with an on/off system, and could save you 10-20% on your heating bill.

Find out more about common problems in gas-combi boilers, or read on for more about how to reduce your heating bill by making the most of your controls.

Heating systems for the 21st century

Most boilers are based on technology that dates back to the 1960s. Colour TV is old news and nobody still cites Twiggy as their celebrity crush, so shouldn’t we bring our heating controls up to date? You could say ‘if it ain’t broke, don’t fix it’ - but it does break, so let’s look at some alternatives.

The modulating room controller

If you’re looking to bring down your gas bills, installing a modulating room controller, either with or without an outdoor sensor, is the smart option for the 21st century.

 This works differently from the traditional ‘on/off’ system. According to Alec, it ‘runs longer at a lower temperature to gently trickle-heat a space, which stops the uncomfortable temperature swings that make you turn up the thermostat’.  Fewer fluctuations in the level at which the boiler fires reduces the amount of energy wasted in heating and reheating your house, which in turn saves you money.

The benefits

  • A modulating room controller could save you 10-20% on your gas bill, depending on use. 
  • They’re surprisingly cheap to install. Alec says it will cost you around £250 or less outside London, assuming your modern condensing boiler is compatible (most are). They are also available with Smart-home heating solutions that use internet controls, such as a Honeywell Evohome expansion pack, and Tado smart thermostats. In both cases the modulating room controller uses the boiler’s digital interface.
  • They’re compatible with most existing boilers. There are a few exceptions, notably some Worcester Bosch models, so check with your Which? Trusted trader whether your boiler can be adapted.

So why don’t we all have one already? The technology required to enable the boiler to ‘know’ when to change heating levels was developed in Glasgow in 1996 and sold to European boiler manufacturers. However, it wasn’t adopted widely in the UK. Alec attributes this lag in uptake to the fact that much boiler manufacture and research takes place outside the UK, together with a reluctance to accept the change away from the on/off system.

Clever controls for smart homes

In a smart home, modulating room controllers can use the boiler’s digital interface, allowing all the temperature information to go on to a central server. This makes it easier to use and more efficient for the consumer.

Somewhat surprisingly, Hive (promoted by British gas) does not use a modulating room controller. While there is definitely a place for app-controlled heating, Alec says: ‘If you are simply using your phone to control an on/off boiler, which fires to a fixed temperature irrespective of heat demand, you’re really not doing as well as you could’. 

Outdoor sensors

Outdoor sensors adjust the boiler’s output based on the outside temperature – less heat on a hot day, for example. These sensors have been mandatory in Germany since 1985 and, as a result, many German boiler brands are designed to work with them. This means UK versions of these boilers may not be working at peak efficiency without the input from an outdoor sensor. 

Outdoor sensors cost up to £500 to install, but can lead to impressive savings.

You can slice up to 30% off your gas bill, subject to variation depending on use.

Improve your boiler efficiency

There are still ways to improve your boiler’s efficiency with more traditional controls. We look at some of these temperature-control methods and assess which will best help you get the most out of your heating system.

Check our article on how to cut the cost of heating your home in winter for more general tips, or read on for more about improving your boiler efficiency using temperature controls.

Thermostatic radiator valves (TRVs)

Found at the end of your radiator, these self-regulating valves control the temperature of a room by changing the flow of hot water to the radiator.

Installation cost: Integrated Heating LTD charges approximately £200 for the first valve, and £20-£50 for subsequent valves. Prices will vary across the UK.

Alec’s advice: ‘These are easy to install. Setting the valves to react to the correct temperature can reduce gas bills. However, if they’re left fully open at all times, they’ll have little effect.’

Efficiency-improvement score: 4.5/10


Zone control

This allows you to control the temperature in different areas of your house, using different ‘zones’ of the heating system. So you can keep your bedroom nice and warm, while the attic is arctic, for example. It’s most cost effective when used with smart thermostatic systems such as Evohome and Tado, when you can use the boiler’s digital controls to make the biggest savings.

Installation cost: The cost will depend on the number of zones, the current wiring in the house, and the size of the house itself.

Alec’s advice: Alec points out that the its expensive to retrofit zone control, unless it’s designed-in from the start in a new home, it’s often not worth it. However, once in place, although the energy savings may be small, they do add up over the years.

Efficiency-improvement score: 2/10 in an average house, possibly more in a large house

Cylinder thermostat

This is a little box with a circular dial that sits on the side of a hot water cylinder, set at a maximum of 60 degrees Celsius. It stops the boiler getting too hot, and shuts it down when required.

Installation cost: This depends on the wiring currently in situ. Cylinder thermostats can be expensive to install – check with your Which? Trusted trader.

Alec’s advice: Most hot water cylinders will already have a cylinder thermostat. If yours doesn’t, it may be too expensive to install one as a one-off. It could indicate that you’ve got an older boiler and you may want to consider upgrading. Check with your Which? Trusted trader.

Efficiency-improvement score: 9/10. Pretty much essential.


Room thermostat

Usually found in the living room or hall, the room thermostat prevents the house from becoming too hot.  Mostly they are ‘fit and forget’ and don’t require much attention. 

Installation cost: On average around £300, depending on the existing wiring in your house.

Alec’s advice: Chances are you’ve got one of these already, but if you don’t you should get one immediately. You can save huge amounts with a room thermostat, as they stop the temperature from climbing too high.

Efficiency-improvement score: 10/10 Crucial. You need this.          

Hot water tank insulation

This is the equivalent of putting a coat on your hot water cylinder, to keep the water inside warmer. It reduces the energy wasted in keeping the water piping hot.  It’s a DIY job, but take care around the hot pipework.

Installation cost: The insulation is reasonably cheap, costing somewhere in the region of £15-20.

Alec’s advice: Modern hot water tanks don’t lose much heat anyway, so it’s probably unnecessary for a modern cylinder. But it can make huge savings on older models.

Efficiency-improvement score: 8/10 Crucial for older cylinders.


Boiler interlock

This ensures the boiler is turned off when there’s no demand for heat, i.e. when the rooms and cylinder are up to the required temperature.

Installation cost: Around £400, depending on the specific wiring in your house. 

Alec’s advice: Alec says boiler interlock is ‘critical’ in any home, as it will keep your energy bills down.

Efficiency-improvement score: 10/10 – essential.

If you’d like to upgrade your heating system, find an accredited boiler installer with Which? Trusted Traders.

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