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How does a thermostat work?

A HomeServe engineer demonstrating how a thermostat works

The humble central heating thermostat, for many of us, is a device that gets set to one temperature and is rarely touched again. However, it’s useful to know what how a thermostat works with your boiler and how you can save on your heating bills just by making small changes to its settings.


Table of contents

  1. What is a thermostat?
  2. How does a thermostat work?
  3. Two main different types of thermostats
  4. What is a smart thermostat?
  5. How to set your thermostat
  6. How to check if my thermostat is working
  7. How does a radiator thermostat work?
  8. How to replace a thermostat
  9. Need a qualified engineer?
  10. FAQs

What is a thermostat?

Your thermostat is a crucial component in the running of your central heating system. In fact, it controls the whole system by reading/sensing the ambient temperature of your household, then switching your boiler either on or off in order to keep it at the temperature you’ve set.

How does a thermostat work?

For example, this means that if you set your thermostat to 21ºC and your home’s temperature drops below 21ºC, the thermostat will switch your heating on to warm it up. When the temperature hits 21ºC, the thermostat will turn off the heating again to avoid wasting energy.

Two main different types of thermostats

What type of thermostat do you have? The two main types of thermostats are:

Traditional analogue temperature dials

A mechanical thermostat uses two strips of metal, laminated together in what’s called a bimetallic strip in the thermostat’s sensor. As the temperature of the house goes up and down the two different types of metal expand and contract, and this switches the electric circuit connected to your heating system on and off.

Mechanical thermostats are less accurate than digital thermostats – sometimes the temperature can vary by as much as 5 degrees – but some homeowners prefer them for their affordability and ease of use.

More modern digital thermostats

Digital thermostats have much more sensitive electronic sensors that read the temperature of the rooms and control the heating to keep it within 1 degree of your chosen setting.

You can also get electromechanical thermostats, which are both mechanical and digital.

For the purposes of setting your thermostat, it’s good to know what type of thermostat you have, and how they send the information to your boiler. For example:

  • Some digital thermostats are wireless and battery-operated
  • Mechanical, and some digital, thermostats are connected with wires to your boiler
  • Programmable thermostats can run the heating at certain times of the day to suit your schedule

What is a smart thermostat?

Digital thermostats include smart thermostats, which are controlled by your smartphone, allowing you to regulate your home’s temperature wherever you are. Some can also use machine learning to adapt to your daily routine. Read our detailed guide to smart thermostats including Google Nest, Ecobee and Hive.

How to set your thermostat

Always follow the instructions or manual that come with a new thermostat. However, below are a few useful tips for how to set your thermostat:

  • Install your new thermostat in an area of the home where air flows fairly freely – the hallway is a safe bet.
  • Make sure it’s a place that is not in constant sunlight – and that it’s not behind a curtain – otherwise it won’t be able to sense the temperature accurately.
  • To set it up, set your thermostat to the lowest temperature you find comfortable. This is about 18 to 21ºC for most people. Remember that every 1ºC that you increase the temperature by, adds around 3% to your heating bill.
  • Don’t touch that dial! You may find it tempting to turn up the thermostat on cold days, but don’t. A thermostat is designed to sense the colder weather and control the heating accordingly. It should regulate the ambient temperature to the one you set. However, you could program the heating to switch on earlier as it may take longer to warm up a house on a cold day.
  • With a programmable thermostat you can set both the temperature and the time, so you can control the temperature at different times of the day. This means you can save energy when you’re at work, but still, time it to switch on just before you return home.

How to check if my thermostat is working

Your thermostat may not be working if there is an issue with the power supply, or if dirt and dust has built up inside the device.

Check the power to the thermostat

1. Check the batteries haven’t run out

Most digital thermostats are powered by batteries (AA or AAA). Replace them with a fresh set and check again.

2. Check the power circuit

If your thermostat is powered by an electrical circuit, check your fuse box or circuit breakers haven’t tripped. If they have tripped, switch them back on and see if your thermostat starts working. If not, you may need to call an electrician.

Clean the thermostat

Dust and dirt can build up inside the thermostat, so it’s good to clean it every so often:

1. Turn off the power to the thermostat’s circuit if it’s on one, or remove the batteries.

2. You can often open up the thermostat, or you may need to unscrew the faceplate to clean it.

3. Clean it gently with a dry, clean paintbrush or similar soft brush. Compressed air also works.

How does a radiator thermostat work?

A thermostatic radiator valve (TRV) is a cylindrical gauge that sits on one side of the radiator at the bottom with numbers usually ranging from 0 to 6. These TRVs allow you to control the set point of each individual radiator you have them fitted to. This means, for example, that you can have all your radiators switched on in the house apart from the ones in rooms that aren’t often used, saving you energy and cash.

How to replace a thermostat

If you want to upgrade an analogue thermostat to a digital or smart thermostat, this is a DIY job that’s strictly not for the novice. It requires second-to-none electrical safety, so never attempt to replace your thermostat if you’re not confident that you know safe protocol around electricity. If you’re a dab hand with a circuit, follow our detailed guide on how to replace a thermostat.

Need a qualified engineer?

We’re on our way. At HomeServe we have teams of Gas Safe registered engineers and Home Experts who can make one-off repairs to your electricity, plumbing and heating system. we’re working with BOXT who offer a speedy boiler installation service – you could be enjoying your new system as soon as the very next day*.

FAQs

How does a thermostat work in a house?

A household thermostat controls your whole central heating system by reading/sensing the ambient temperature of your household, then switching your boiler either on or off in order to keep it at the temperature you’ve set.

How does a thermostat function?

An analogue thermostat contains metal strips that expand and contract and switch your heating on and off. A digital thermostat has a more accurate electronic sensor.

Do you turn the thermostat up or down for cold?

Once your thermostat has been installed, set it to the lowest temperature you find comfortable. For most people, this will be between 18 and 21ºC. You shouldn’t have to touch it – it’s the thermostat’s job to keep the temperature at your chosen setting.

*Subject to engineer availability

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About the author

Chris became a fully qualified Gas Engineer in 2009 and has been with HomeServe since 2016. Chris hung up his tool bag in 2018 to concentrate on ways to use technology to help Customers.

He currently heads up the Self Fix team who are able to get Customers back up and running over the phone without the need for an Engineer.

He is kept busy looking after his two daughters and is a lover of all things CrossFit, Yoga and Ice Baths!

“I chose to work at HomeServe after running a small business. I wanted to be able to help people on a greater scale and HomeServe has helped me achieve that.”

Qualifications

Gas Safe registered, CCN1, CPA1, CENWAT, CKR1, HTR1, NVQ Level 3 Plumbing & Heating

Years qualified

Since 2009
Read more

Share this post

About the author

Chris became a fully qualified Gas Engineer in 2009 and has been with HomeServe since 2016. Chris hung up his tool bag in 2018 to concentrate on ways to use technology to help Customers.

He currently heads up the Self Fix team who are able to get Customers back up and running over the phone without the need for an Engineer.

He is kept busy looking after his two daughters and is a lover of all things CrossFit, Yoga and Ice Baths!

“I chose to work at HomeServe after running a small business. I wanted to be able to help people on a greater scale and HomeServe has helped me achieve that.”

Qualifications

Gas Safe registered, CCN1, CPA1, CENWAT, CKR1, HTR1, NVQ Level 3 Plumbing & Heating

Years qualified

Since 2009
Read more

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