A DS18B20 probe on the Plus Add-on shows N/A, never appears, or reads the wrong number. Check the Add-on is switched on, the probe is added, and where the Shelly sits.
Checked
Gen4
Start here
What are you seeing?
Pick the closest match and we'll point you to the fix most likely to sort it.
The Plus Add-on clips onto a Shelly 1, 1PM or 2PM Gen4 and reads up to five
DS18B20 temperature probes. The relay has to be told the Add-on is there, and
each probe added on its own.
When a probe shows N/A, the Shelly knows about it but can't get a reading. That
comes down to the probe, its connections or the heat around the Shelly.
Before you start
These checks are done on the device's web page or in the app. The Add-on plugs onto a relay that carries mains, so checking or reseating it, or the probe's connections, is a job for a licensed electrician with the power off. Don't open the wall plate.
Quick checks first
Run these checks before moving on to the fixes.
Checklist0 of 2 checked
Check the Add-on page
On its web page, click Add-on. Your probes are listed under Peripherals, each with its reading. N/A with a red read tag means no reading.
Check where the Shelly is
Shelly rates the relay and the Add-on for up to 40 °C around them. Only the probe belongs in a roof space or other hot spot.
Fixes, most likely first
Work down the list and stop when it's fixed.
1
Most likely for you
The Shelly can't read the probe
How to tell. The probe is listed under Peripherals but shows N/A. Shelly says N/A means the sensor can't retrieve a value or isn't working properly.
Restart the device
On its web page, go to Settings and click Reboot, then check the reading again.
Check it isn't overheating
If the relay and Add-on sit in the roof space with the probe, they're outside their 40 °C rating on a hot day. Moving them is a job for a licensed electrician; only the probe needs to stay in the roof.
Ask an electrician to check the connections
If it still shows N/A, the Add-on's seating, the probe's connections or the probe itself need checking with the power off. That's a job for a licensed electrician.
Did this fix it?
2
Most likely for you
The Add-on isn't switched on
How to tell. The Add-on page has None picked, and there's no Peripherals section to add a probe to. The device only uses the Add-on once it's enabled and restarted.
Choose Sensor Add-on
On its web page, click Add-on, pick Sensor Add-on and click Save and reboot. In the app, it's the Add-on peripherals tab.
Did this fix it?
3
Most likely for you
The probe was never added
How to tell. The Add-on is on, but the probe isn't listed. Switching the Add-on on doesn't create any sensors; each probe is added on its own.
Add the probe
On the Add-on page, click the + beside Peripherals, choose the DS18B20 temperature sensor, tick the probe it finds (Rescan if it doesn't), then add it and reboot.
One at a time in the app
The app adds one peripheral at a time, with a restart after each.
Did this fix it?
4
Most likely for you
A new probe replaced the old one
How to tell. After swapping a probe, the old entry shows N/A. Each entry is tied to one probe's address, so a new probe isn't linked to it.
Note its settings first
Shelly warns that deleting a peripheral removes it and all its actions for good. Note its name, offset and any actions first.
Delete the old entry and add the new probe
On the Add-on page, click the bin beside the old entry. Then click the + beside Peripherals to add the new probe, and reboot.
Did this fix it?
5
Most likely for you
A DHT22 is set up as well
How to tell. A scan for DS18B20 probes finds nothing while a DHT22 humidity sensor is set up. Shelly supports up to five DS18B20 probes or one DHT22, not both.
Pick one type
Delete the DHT22 entry and reboot before scanning for DS18B20 probes. Rewiring between the two is a job for a licensed electrician.
Did this fix it?
6
Most likely for you
The offset or threshold is off
How to tell. A reading shows but it's shifted, or it won't change until the temperature moves a lot. Offset adds to every reading, and the threshold sets how far it must move before it reports.
Check Offset and Delta Threshold
On the Add-on page, click the pencil beside the probe. Set Offset to 0 unless you added it on purpose. Delta Threshold runs from 0.1 to 5 °C; a low value reports smaller changes.
Did this fix it?
7
Most likely for you
The model doesn't take the Add-on
How to tell. There's no Add-on page at all. Shelly lists the 1, 1PM and 2PM Gen4 as Plus Add-on hosts. The Dimmer Gen4 is not supported, and the Mini models aren't on the list.
Use a supported host, or another sensor
A Plus Uni takes the same probes on low voltage, or a BLU H&T reports temperature with no wiring. Changing the device is a job for a licensed electrician.
Did this fix it?
Frequently asked questions
Up to five DS18B20 probes, or one DHT22.
Yes. Shelly says deleting a peripheral removes its actions and settings, and they can't be brought back.
Adding or removing a peripheral changes the device's components, and Shelly needs a restart to apply that.
