A few weeks ago my boiler started to show a S30 No Heat Demand from Control Unit error and the boiler would not fire up when the room temperature dropped below the Nest thermostat set point. After some trial and error, I found that pushing the heatlink button to switch to manual did instantly fire up the boiler and after a few minutes I could put it back to auto and the thermostat would control the boiler without manual intervention. After a few days the same problem would occur, and the same solution would get it back into sync. Fast forward and we are now away. The Nest thermostat is set to Eco and yet the room temperature is way above the setpoint. It is as though the boiler is not stopping to fire when it should and yet usage according to the App is reportedly zero. However, there is no way that the house temperature is what is being reported through the app.
Any thoughts on whether this is a Nest thermostat problem, a Heatlink problem, or a boiler problem?
