If your boiler thermostat isn’t working, first work out which thermostat you mean. The room thermostat switches the heating on and off by air temperature, while the boiler thermostat (the flow temperature dial on the boiler) sets how hot the radiator water gets. Most faults are with the room thermostat, and they nearly always come down to flat batteries, a lost wireless pairing or the wrong settings, all of which you can sort yourself.
We’re Clever Energy Boilers, Gas Safe registered (no. 554138) and accredited Worcester Bosch installers based in Bingley, fitting new boilers and controls across Yorkshire, the North West and the Midlands. We’ve completed more than 25,000 installations in the last 15 years. This guide shows you how to tell the two thermostats apart, a 60-second test for whether the boiler is getting a call for heat, and the checks that are safe to try.
Which thermostat is it?
You’ve got two controls doing two different jobs. Mixing them up is one of the commonest reasons people think their heating has broken when it hasn’t. Here’s how they compare:
| Detail | Room thermostat | Boiler thermostat (flow temperature) |
|---|---|---|
| Where it is | On a wall in your home, or a smart thermostat on a stand or wall | On the boiler itself, as a dial or on the display |
| What it does | Turns the heating on and off depending on how warm the room is | Sets how hot the water going to your radiators gets |
| Typical setting | 18 to 21°C, which the Energy Saving Trust says most people find comfortable | Not below 65°C if you have a hot water cylinder, because of the legionella risk |
| Who can fix it | Usually you: batteries, settings and pairing | Boiler-side sensor faults need a Gas Safe registered engineer |
Turning the room thermostat right up doesn’t heat the house any faster. It just keeps the boiler running until the room reaches that temperature, while the dial on the boiler decides how hot the radiators run in the meantime.
How can I tell if my boiler is getting a call for heat?
Run the 60-second test. It tells you whether the problem sits with the thermostat or the boiler:
- Check the boiler first. Make sure it has power, the pressure looks normal and there’s no fault code on the display.
- Turn the room thermostat up by 3 to 5°C above the current room temperature.
- Look at the receiver if your thermostat is wireless. On a Hive receiver, the status and heating lights should both be green.
- Listen for the boiler firing. Give it a couple of minutes before you decide nothing’s happening.
Then match what happened to this table:
| What happens | What it means | What to do next |
|---|---|---|
| The boiler fires up | The thermostat and boiler are talking. The problem is somewhere else in the system | See hot water but no heating or radiators not heating up |
| Thermostat and receiver look normal, but the boiler doesn’t fire | The signal is probably getting through, so the fault is likely on the boiler side | See boiler not firing up, then a Gas Safe registered engineer |
| Thermostat screen blank, or the receiver shows no signal | The thermostat isn’t sending a call for heat | Work through the thermostat checks below |
Why is my thermostat not working?
These are the usual causes, easiest to sort first.
Are the batteries flat?
A blank screen on a wireless or battery thermostat nearly always means flat batteries. Fresh ones should bring the display straight back.
Has the wireless thermostat lost its pairing?
Wireless thermostats talk to a receiver wired into the boiler. If the two lose their connection, the boiler never gets the signal to heat. On Hive this shows as a “No RF” message on the thermostat, and other makes show a no-signal symbol or something similar. Re-pairing usually fixes it, using the steps further down.
Is the thermostat in the wrong place?
A thermostat next to a radiator, above a fire or behind curtains reads the wrong temperature. It can think the room is warm while the rest of the house is cold, and switch the heating off too soon. A badly placed thermostat is also one of the causes of boiler short cycling.
Are the settings or schedule wrong?
Rule out the simple things before anything else. The schedule might be set to off, the clock might be wrong, or the set temperature might be below what the room already is. If your heating keeps switching off at odd times, our guide on why a boiler keeps turning off covers the other reasons.
Is the wiring loose or failed?
Wired thermostats and receivers can develop loose or failed connections. If the thermostat has power but nothing reaches the boiler, wiring is a likely cause, and it’s a job for a qualified engineer rather than a DIY fix.
Is the smart hub or Wi-Fi offline?
Smart thermostats rely on a hub and your home Wi-Fi for the app and schedules. An unplugged hub or a dropped connection can leave the app unable to control the heating, so check the hub has power and the router is working. Our comparison of Hive vs Nest thermostats and our guide to how smart thermostats cut your heating bills explain how these systems work.
Is a boiler sensor at fault?
If the room thermostat and receiver are fine but the boiler still won’t respond, or runs too hot, a temperature sensor inside the boiler may be the problem. That needs a Gas Safe registered engineer. Never take the boiler casing off yourself.
What can you safely check yourself?
- Change the batteries, even if the screen still shows something.
- Check the receiver lights. On Hive, the status and heating lights should both be green.
- Re-pair the thermostat by following the manufacturer’s steps. For Hive, take out a battery, power-cycle the boiler, put the receiver into pairing mode, then hold the plus and minus buttons until “FIND” appears.
- Turn the thermostat up by 3 to 5°C and listen for the boiler.
- Look at the schedule, and on a smart thermostat check the hub and Wi-Fi too.
Is a faulty thermostat dangerous?
A room thermostat fault on its own isn’t a safety problem. It leaves you with heating that won’t come on, or won’t go off when it should. A fault on the boiler side is a different matter, and anything behind the casing is for a Gas Safe registered engineer only.
What temperature should I set my thermostat to?
The Energy Saving Trust suggests most people are comfortable with the room thermostat at 18 to 21°C. In a draughty stone terrace in Keighley or Haworth during a Yorkshire winter, you’ll probably sit nearer the top of that range.
The boiler thermostat is separate. If you have a hot water cylinder, don’t set the flow temperature below 65°C, because of the legionella risk. If you’re not sure which system you have, our guide to the types of boilers explains the difference.
What does a thermostat repair or replacement cost?
Thermostat prices below come from MyBuilder:
| Job | Typical UK cost |
|---|---|
| Manual or programmable thermostat, fitted | £100 to £200 |
| Smart thermostat, fitted | £150 to £300 |
| Rewiring or a faulty receiver | Engineer to quote after diagnosis |
| Boiler-side sensor fault | Gas Safe registered engineer to diagnose and quote |
If the 60-second test points to the boiler rather than the thermostat, a new thermostat won’t fix it.
Should I repair it or replace the boiler?
Replace the thermostat if the thermostat is the problem, because it’s the cheap part. The bigger decision comes when the fault is on the boiler side. On a boiler of 8 years or more, a boiler replacement usually makes more sense than another repair, and older boilers may not be compatible with modern smart or load-compensating controls anyway.
A new boiler can come with matched controls, including smart thermostats, set up to work together from day one. You’ll have long, market-leading warranties available through Clever Energy, and you can spread the cost with boiler finance. Our guides on when a boiler needs replacing and how much a new boiler costs will help you decide.
Boiler thermostat FAQs
How do I know if my thermostat or my boiler is the problem?
Do the 60-second test. If the boiler fires when you turn the thermostat up by 3 to 5°C, the thermostat is working, and if it stays silent while the thermostat and receiver look normal, the fault is likely on the boiler side.
Why is my thermostat screen blank?
Usually flat batteries. If a wired thermostat stays blank, it may have lost power or developed a wiring fault, which needs an engineer.
How do I re-pair a wireless thermostat?
Follow your manufacturer’s steps. On Hive, remove a battery, power-cycle the boiler, put the receiver into pairing mode, then hold plus and minus on the thermostat until “FIND” appears.
What temperature should I set my thermostat to?
18 to 21°C for the room thermostat, as the Energy Saving Trust suggests. On a system with a hot water cylinder, keep the boiler’s flow temperature at 65°C or above.
Can a faulty thermostat stop hot water?
Not on a combi, because the room thermostat only controls the heating. With a cylinder, its own timer or thermostat can be the cause, and our guide to heating working but no hot water covers both setups.
Get a new boiler with Clever Energy
We fit new boilers and controls in Bingley, Bradford, Leeds, Keighley, Halifax and across Yorkshire, the North West and the Midlands, from Manchester and Liverpool down to Birmingham and Leicester. Start with our boiler installation page, or compare Worcester Bosch, Vaillant, Ideal and Baxi installation. Get your fixed online boiler quote in a few minutes, or request a callback if you’d rather chat first. Once it’s in, a Clever Care plan keeps your new boiler protected.