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How to replace a Danfoss FP715Si with smart heating controls

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UKPublished 6 October 2026 · Written by BuyMeWhiskey Editorial Team · How we check facts

A smart replacement should be chosen by the heating system and wiring, not simply by the old controller's brand. Before buying, confirm the heat source, switching arrangement and compatibility with the existing system.

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Use the Energy Saving Trust heating-controls guidance to understand the control type your system needs before choosing a replacement.

Read Energy Saving Trust heating-controls guidance

Identify the heating system first

A programmer that works perfectly with one heating system may be the wrong choice for another. Before replacing an older Danfoss controller, identify whether the property has a conventional boiler, a system boiler, a heat pump, electric panel heaters or storage heaters. Then identify whether the existing control is switching a heating circuit, a hot-water circuit, or both.

Energy Saving Trust describes heating controls broadly as programmers, thermostats and thermostatic radiator valves that manage when heating operates and how warm the home becomes. Smart controls add connectivity or automated scheduling, but they still need to be appropriate for the underlying system.

Compatibility is more than “will it fit on the wall?”

The important questions are electrical and functional. Check the voltage and switching arrangement, the number of channels, whether a room thermostat is already present, and whether your boiler or other heat source supports the control method. Physical dimensions are the easy part; correct wiring is the part that can make a device unsuitable.

Do not assume a modern smart thermostat can simply replace any old programmer without checking the manufacturer's wiring instructions. Some systems need a compatible receiver or an installer to alter the control arrangement.

For boilers, separate time and temperature controls

Ofgem's current energy-price information shows why heating control is worth considering: from 1 October to 31 December 2026, the average direct-debit cap unit rates are 26.32 pence per kWh for electricity and 7.97 pence for gas, although actual prices vary by region, tariff and usage.

Energy Saving Trust says effective heating controls could save around £100 a year in Great Britain and £110 in Northern Ireland. That is an indicative saving, not a guaranteed result. Homes differ, and a household already using its existing controls efficiently may save less.

Storage heaters need a different approach

Modern storage heaters can have automatic charge control, thermostats and programmers, while older models may use manual input and output dials. Energy Saving Trust says storage heaters charge during off-peak periods on relevant tariffs and release stored heat later.

So a smart control designed for a gas boiler is not automatically the right answer for electric storage heating. Check the heater manufacturer's instructions and the tariff arrangement before changing the controls.

What a smart controller can actually add

Remote scheduling when you are away.
Automatic time and temperature adjustments.
Some systems learn routines or use occupancy information.
Clearer visibility of the programmed schedule.
Potential integration with other home controls.

The benefit is normally better control, not magic efficiency. A smart device cannot make an inefficient heating system efficient by itself, and it cannot recover money that is wasted because the home is heated more than necessary.

DIY or installer?

If the replacement involves mains wiring or changes to the heating control circuit, use a suitably qualified installer unless you are competent to do the work safely. A smart product's app setup is easy; the electrical and heating-system compatibility is where errors become expensive.

Keep photographs of the old wiring before removal, but do not treat a photograph as a substitute for a wiring diagram. The electrician or heating professional should work from the manufacturer's instructions and the actual system configuration.

Check the tariff as well

For storage heating, the tariff can affect how and when the heater should charge. Energy Saving Trust notes that storage-heater behaviour depends on the heater model and electricity tariff. If your property still uses an older off-peak arrangement, verify how the meter and control signal operate before replacing equipment.

Compare the cost with the realistic saving

If a control upgrade costs money, compare the installed cost with a realistic saving estimate rather than the best-case marketing claim. Energy Saving Trust's around-£100-a-year figure is a useful reference point, but your own usage and system matter.

Before ordering

Identify the heat source.
Identify the current programmer, thermostat and wiring arrangement.
Check the new controller's compatibility list.
Check whether an installer is needed.
Compare the installed price with your likely saving.
Confirm how the control will interact with your tariff and meter.

Illustrative smart-control payback

Worked example

Illustrative payback example: suppose a smart-control upgrade costs £300 installed and the household estimates it will reduce its heating cost by an illustrative 8%. If the relevant annual heating spend were an illustrative £1,200, the saving would be £1,200 × 0.08 = £96 a year.

Illustrative annual saving: £96.
Illustrative simple payback: £300 ÷ £96 = 3.125 years.

This is not a predicted saving. Energy Saving Trust says effective heating controls could save around £100 a year in Great Britain, but actual savings depend on the home, system, controls already installed and how the household uses heating.

The saving estimate is an indication, not a guarantee. Your result could be smaller if the old system was already well controlled, or different if the household changes its heating pattern after installation.

Can I replace a Danfoss FP715Si with any smart thermostat?#

No. Compatibility depends on the heating system, wiring, channels and the controller’s electrical and functional requirements. Identify the existing setup and follow the new control’s wiring and compatibility instructions before buying. The physical controller is only one part of the overall heating-control setup.

Do smart heating controls save money?#

They can. Energy Saving Trust says using heating controls effectively could save around £100 a year in Great Britain, but that is an indicative figure rather than a guarantee. The saving depends on how well the existing system is already controlled.

Can a smart thermostat work with storage heaters?#

Not automatically. Storage heaters have charging and heating phases and may depend on an off-peak tariff or control signal. Energy Saving Trust recommends using guidance specific to electric storage-heater controls rather than treating them like boiler controls. Confirm the supply and control arrangement before changing any wiring.

Should I replace the programmer and thermostat together?#

Sometimes that is sensible, but it depends on the system. A replacement can be worthwhile when the existing controls are limited or incompatible with the desired smart setup. Check whether the new product can use the existing thermostat or requires a matching receiver.

What should I check before installing a smart controller?#

Check the heat source, wiring arrangement, number of heating and hot-water channels, existing thermostat, manufacturer compatibility list and whether professional installation is recommended. Also check how the device interacts with your electricity tariff if the heating is storage-based. Smart scheduling can improve control, but it does not create heat more cheaply on its own.

Are heating controls worth installing in 2026?#

They can be, particularly where heating schedules are poor or the existing controls are old. Energy Saving Trust says effective controls can save around £100 a year in Great Britain, while Ofgem’s 2026 energy-price data shows that unit costs remain material. Compare the installed cost with your expected use.

What if the controller looks compatible but the wiring is different?#

Stop before connecting it. A physical match is not proof of electrical compatibility. Use the manufacturer’s wiring diagram and, where the work involves mains wiring, a suitably qualified installer. Incorrect wiring can damage equipment or create a safety risk.

Keep reading

Next question →How do you convert a gas meter reading to kWh?

Sources

Figures were checked against these sources before publication. If a rule changes, we update the page and show the new date.

General information, not personal financial advice. Rules depend on your circumstances; check the official source or speak to a regulated adviser before acting.