Hello, after months of struggling with my Nest gen3 EU in TrueRadiant setting, i discovered a thing that is missing in the Nest settings, and is really required to make TrueRadiant work with the new generation of efficient modulating low temperature heaters/boilers:
I have a house with regular radiators, and a gas-powered heater/boiler. The Nest is connected through OpenTherm(OT) and i have TrueRadiant enabled to make sure heating is as efficient as possible.
The reality is that the new generation of modern heaters have a minimum power (kW) that is, even at the lowest setting, already hotter than what the Nest TrueRadiant algorithm is requesting for water-temperature when it's getting close to the requested temperature (setpoint).
F.e. in my case, when TrueRadiant detects it's close to setpoint, it requests a lower temperature water, about 40 degrees Celcius. But with a radiator-based system, this is simply to low to heat up the radiators effectively. What happens is that the radiators stay to cold, the house doesn't heat up to the target temperature, and the heat cannot get out of the heater/burner, which will shut down when there is to much heat building up inside.
After a safety period, the heater will try again, as the TrueRadiant algorithm is still trying to increase the heat by requesting low-temp water, and the same thing will happen over and over again: radiators not heating up enough (they typically need around 50 degrees C of hot water flowing through them at a minimum to do their job), and the boiler shutting down due to internal overheating.
The solution is simple: set a minimum temperature threshold for the requested water temperature. Some newer/more advanced heaters/boilers (like my Intergas Xtreme 30) have the option in their advanced service menu to increase this threshold. But not all (most?) heaters have this.
So, it would be the best option if you could set this minimum requested water temperature in the Nest TrueRadiant settings. This will solve a lot of problems.
So my suggestion to the Google Nest team is to add this feature to the TrueRadiant settings, maybe in an advanced/pro menu, which could also include max thresholds, temp sensor offsets, reset learning data (as this is not possible, even with a full factory reset) etc.
NB It's my take that the TrueRadiant algorithm was designed with floor-heating systems, which run at a much lower water-temperature. For radiators (classic ones, not the more modern low-temp ones, that need a very good isolated space anyway) this minimal temperature that is requested by TrueRadiant is simply way to low, and will shut down the system.
