Boiler runs uncontrolled for hours due to SAT low setpoint behavior #131
Description
Issue:
The problem occurs when the SAT provides a low setpoint (between 10.2 and approximately 20°C). The boiler obviously cannot deliver this and instead supplies water that is too hot. Rather than switching to low-power delivery, the SAT continues to request heat. As a result, the boiler can remain on for hours with ever-increasing heating temperatures (far above the thermostat setpoint)
Setups
This problem occurs on two different systems: one with underfloor heating and one with radiator heating. Direct control via OTGW. No other thermostats involved
Settings
For both systems the same:
- 3 Duty cycles per hour
- Dynamic minimal setpoint `-> boiler temperature
- Coëfficiënt curve: between 2,5 and 5. This problem occurs with both setpoint values, but it happens more frequently at lower values than at higher ones. The downside of higher values is, of course, a significantly higher gas consumption.
See attached picture:
During the first 20 minutes, the system behaves as expected—the water temperature fluctuates around the setpoint. After this period, however, the setpoint drops to a level that the boiler cannot achieve. Normally, the SAT would switch to a low-load mode, but in this case, it enters an abnormal state that persists for hours. In most cases, the only solution is to reset the SAT or lower the room setpoint by 2–3 degrees.
