According to building regulations, your boiler system requires a minimum set of controls and these include boiler interlock, room thermostat, programmer, thermostatic radiator valves and a hot water cylinder thermostat. We’ll look at all of these things individually and how they can control your boiler system to make sure you’re not overheating your home. 

Boiler interlock

Boiler interlock isn’t a physical control device. Instead it describes how the system has been wired in. It’s a wiring arrangement that prevents your boiler from heating your home when there’s no need for it, for example, if the temperature that you set on the thermostat has been reached.

Without interlock, the boiler would be on continuously, which could waste a lot of energy. For combi boilers, interlock is usually achieved by using a room thermostat. This could include a standard or digital thermostat. Programmable thermostats and time switches should be wired so that they are interlocked with the boiler and the pump too.

Room thermostat

The room thermostat is usually positioned in a central location, such as a living room or hallway, and should be sited around one and a half metres above floor level. It’s better if it isn’t installed in a kitchen as this room can become naturally warm through cooking. The thermostat senses the temperature of the air flowing around it and sends a signal to the central heating pump and boiler to stop heating. It’s an important element and, without it, boiler interlock would not function properly.

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Thermostatic radiator valves (TRVs)

A TRV is a self-regulating valve that adjusts the flow of water into your radiator depending on which setting you have it on. If you set your radiator to number three, your room will average around 20°C. TRVs should be installed with a room thermostat to provide boiler interlock.

TRVs shouldn’t be installed on bathroom radiators or towel rails. This is because the temperature and humidity can fluctuate so much in your bathroom that the TRV will turn the flow off when you potentially need the heat from the radiator to help to get rid of the condensation.

Electronic TRVs are becoming increasingly popular as they can be used with your smart heating system, such as tado°. They allow you to set each room at its own temperature. For example, if you prefer your bedroom to be cooler than your living room, you can set these parameters to suit you. These temperatures can all be set from your mobile phone or tablet.

Hot water cylinder thermostat

A hot water cylinder thermostat works by sensing the temperature of the water inside the cylinder. It’s able to signal to the boiler to turn on when the temperature falls below the thermostat setting and to turn off once the right temperature has been reached.

You shouldn’t alter your thermostat in the hot water cylinder. Setting it to a higher temperature will not make the water heat up faster. Instead, you should think about the times you’re likely to use water the most. For example, if you have a shower in the morning and your partner has a shower in the evening, it would be most beneficial to set the hot water to come on before you get up, giving it enough time to heat the water before your shower. You should then set the hot water to come on again later on, in time for doing the dishes after tea and having evening showers.

How to save energy with an interlock switch

All of the controls that we’ve mentioned above will make your heating system operate as efficiently as possible, and therefore could reduce your energy costs.

To save as much money on your heating as possible, you could reduce your thermostat by one degree. When your home reaches a set temperature, the interlock will automatically stop your boiler from firing. If you set your home’s internal temperature to 20°C instead of 21°C, for example, your boiler doesn’t need to be on for as long because your home will reach the lower temperature more quickly. You could save £85-90 per year by reducing your thermostat by one degree.

You could also save money by moving your digital thermostat away from lamps, TVs or other devices that could affect the temperature it’s sensing. Room thermostats will be situated on a wall and cannot be moved, but digital thermostats can be placed anywhere. You should also make sure that it isn’t in direct sunlight. These issues could make the thermostat take a false reading for the actual room temperature and it will force the boiler to shut down. Then, when the temperature drops again, it will start the boiler up. This constant on and off motion will waste energy as your boiler is always having to restart.

What is an interlock switch?

An interlock switch is different from boiler interlock, but it works in a similar way. Interlock switches interrupt the electrical current that’s running around a circuit and are a safety device on machinery and industrial equipment, such as elevators. For example, a machine guard could be interlocked, which means that the equipment cannot operate until the guard is in position. If the guard is removed during operation, the machine will shut down.

Interlock switches shouldn’t be confused with standard safety switches. For example, a switch on a microwave that stops the door from opening while the microwave is in use isn’t an interlock. However, it would be considered an interlock if the microwave was unable to work while the door is open. 

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