Impact of the room temperature gain factor

Parameter 750 determines the room temperature gain factor ("Raumeinfluss") for heating circuit 1. There are similar parameters for the other heating circuits, but they all work the same – if you know how, that is, because the percentage that can be set between 0% and 100% actually has a much stronger influence than one might expect. So when I saw that my heater was not really behaving the way it should, I tried to figure out more about how this parameter influences the flow temperature ("Vorlauftemperatur").

I noticed that something was off when my boiler always ran at 100% when there was a reasonably significant room influence and then switched off immediately when the room temperature was reached without modulating much. Now I have found the formula(s) in various sources according to which the room temperature gain factor affects the flow temperature as follows:

dTV = dTRw * (1 + s)
where:
dTV = resulting flow temperature deviation
dTRw = room setpoint correction
s = heating curve slope (parameter 720)

The room setpoint correction dTRw is calculated as follows:
dTRw = dTR * room influence (parameter 750) / 10
where:
dTR = Difference between actual room temperature and room temperature setpoint

The formula can then be summarized as follows:
dTV = dTR * room influence / 10 * (1 + s)

With a heating curve of 1.5 and a difference between actual and setpoint room temperature of 2 degrees and a room temperature influence of 25%, this means

dTV = 2 * 25 / 10 * (1 + 1.5) = 12.5 °C change in flow temperature

With a deviation of 4 °C (e.g. at the end of the night setback), the flow temperature would already be 25 °C higher, which is probably more than what would be chosen for rapid heating (parameter 770). The boiler also switches off when the room temperature limit (parameter 760) is reached, even if the room temperature gain factor is only 1%. For me, this means that I will set the influence to a maximum of 20%. Perhaps even 1% is enough if the heating curve as such is adequately chosen and the room temperature gain factor is then only used to switch off the heating when the room temperature limit is reached.

I have created a small Excel sheet in which you can quickly explore the effects on the flow temperature using your own values for room temperature deviation, gain factor and heating curve slope.