The short answer
Check whether the heating still works from the thermostat itself. If the buttons control the boiler but the app says offline, it is purely a Wi-Fi problem and your heating is safe. If the thermostat is blank, it is a power problem at the receiver or the batteries.
The first thing to establish is whether you have a heating problem or an internet problem, because they feel identical in the app and are completely different in seriousness.
Separate the two
Walk to the thermostat and turn the temperature up manually. If the boiler fires, everything mechanical is fine and you are dealing with a connectivity issue — annoying, not urgent, and your heating will keep following its existing schedule. If nothing happens, the problem is between the thermostat and the boiler.
If it is a Wi-Fi problem
Check whether anything else changed
A new router, a changed Wi-Fi password or a provider swap will knock every smart device offline at once. If other devices are also offline, that is your answer and each will need reconnecting.
Restart the thermostat and the router
Unplug the router for 60 seconds. Restart the thermostat through its menu, or by removing and refitting it from its wall plate, or by pulling its batteries.
Check the signal where the thermostat is
Hallways, cupboards and boiler rooms are exactly where signal is worst, and thermostats have small antennas. Stand at the thermostat with your phone and run a speed test.
Confirm it is on the 2.4 GHz band
Nearly all thermostats are 2.4 GHz only. If your bands share one name, split them and reconnect the thermostat to the 2.4 GHz network specifically.
Check the bridge or receiver, not just the thermostat
Many systems use a separate hub or a receiver box near the boiler, and that is the part that actually connects to your network. If your system has one, its lights are the ones to read.
Reserve its IP address
Once reconnected, assign a fixed address in the router so it does not lose its place again.
If the thermostat is blank or unresponsive
- Battery models — replace the batteries, and use good quality alkalines. Rechargeables often lack the voltage these units expect.
- Wired models — check the fused spur near the boiler and the boiler’s own power. A tripped breaker takes out the receiver and the thermostat together.
- Check the receiver’s lights by the boiler and compare them with the manual, which will name the fault.
Replacing batteries, restarting units and reconnecting Wi-Fi are all fine to do yourself. Anything involving wiring at the boiler or the receiver, or removing covers from the boiler itself, is work for a qualified heating engineer. If you have no heating and no hot water in cold weather, treat it as urgent rather than a DIY project.
Keeping the heating running meanwhile
Almost every smart thermostat keeps its schedule locally, so an offline unit continues heating to plan — you simply lose remote control. Most systems also have a manual override or a boost button on the receiver, and knowing where that is before you need it is worth five minutes now.
Frequently asked questions
Will my heating still work if the thermostat is offline?
Usually yes. The schedule is stored on the device and keeps running; you lose app and voice control, not the heating itself.
Why did my thermostat go offline after I changed router?
It is still looking for the old network name and password. Every smart device needs reconnecting after a router change, and the thermostat is often the one people forget.
How long do thermostat batteries last?
Typically one to two years with good alkalines. A thermostat that loses connection intermittently before going blank is often showing early battery decline.
Can I control the heating without the app?
Yes. The thermostat itself works normally, and most systems have a manual override on the receiver by the boiler. It is worth locating that control before you need it.
Check whether the boiler responds to the thermostat itself. That one test tells you whether this is urgent or merely irritating.
