Netatmo Thermostat shows heating active but boiler does not fire after long standby
Hello, I am experiencing an intermittent issue with my Netatmo thermostat connected to an Airfel boiler (On/Off dry contact connection).
Here is the problem:
• When I set the temperature from 18°C to 22°C, the thermostat shows “heating active” in the app.
• However, the boiler does not fire.
• If I turn the boiler off and on (power reset) or reset it manually, the system starts working normally.
• After that, everything works correctly for 1–2 days. The issue usually happens in this scenario:
• I leave home and set the thermostat to 16°C.
• The house stays above 16°C for 2–3 days, so there is no heating demand.
• When the temperature finally drops below 16°C, the app shows heating active, but the boiler does not start.
• Again, resetting the boiler fixes the issue. Important details: • If I remove the thermostat wires and manually short the RT (room thermostat) terminals on the boiler, the boiler fires immediately. • The thermostat is connected via dry contact (COM and NO).
• The relay is powered inside the boiler. It seems like after a long standby period, the relay might not properly close the contact even though the app shows heating demand. Could this be a relay contact issue or a power supply problem?
Thank you.
Comments
7 comments
Since your Relais is connected to the boilers power supply, it also restarts when you power cycle the boiler, right?
Have you tried only power cycling the Relais to check if everything works again as well?
Thank you for your reply.
Yes, the relay is powered from inside the boiler, so when I power cycle the boiler, the relay also restarts.
I have not tested power cycling only the relay separately, because it is connected to the boiler’s internal power supply.
I see.
Would be interesting to see what would happen if you did to narrow things further down.
However Relais hardware defect seems most likely. If you‘re still in the warranty period I would suggest you contact your reseller for a replacement.
If not, submit a request to Netatmo support on the bottom of this page:
https://helpcenter.netatmo.com/hc/en-us/articles/360026110232-My-heating-system-doesn-t-respond-to-commands-from-the-Thermostat-what-should-I-do
Thank you for your suggestion.
One thing I am trying to understand is this:
If the relay has a hardware defect, why does the system start working normally again after I completely power cycle the boiler (which also cuts power to the relay)?
After a full power reset, the relay works perfectly for 1–2 days until the next long standby period.
Would a hardware defect typically behave like this — temporarily fixed by cutting power — or could this indicate a firmware or power supply stability issue instead?
Thank you for your insight.
That’s why I asked if both boiler and Relais were on the same breaker, to know if only the boiler restarted or the Relais as well. To rule out a boiler defect (otherwise than you already did with jumping out the contacts 👍) would be to power cycle the Relais alone.
As to what causes this behavior, well electronic stuff sometimes is unpredictable. Maybe some transistor does something it’s not supposed to and emptying its charge temporarily fixes it. I can’t say, I‘m not an electrical engineer, sorry.
Do you actually have the Modulating Thermostat (which this part of the Community is for) running in Dry-Contact mode or just the normal Smart Thermostat?
I am using the standard Smart Thermostat in dry-contact (On/Off) mode.
It is not a modulating (OpenTherm) setup.
The relay is connected via COM and NO to the boiler’s RT terminals.
Thanks for clarifying.
I‘ve moved this topic to the „Smart Thermostat“ section.
Fulfilling my Community-Janitor duties 😋
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