Viessman Vitodens 200W: Fault EE / Unstable room temp / Can't set some temperatures

lanem2494

pbrisbin said:

3- Can't set some temperatures

This is as simple as it sounds. I literally cannot set the room temperature to certain temperatures. If I move the dial to 60F and press OK, when I go back and look it's back to 61F. It seems to require odd temperatures. If I move it to 58F, press OK, when I go back and look it's shifted to 59F. Same thing happens with reduced room temp. At higher temperatures, it seems to want evens. If I move it to 67F and press OK, when I look again it's shifted to 66F or 68F (depending on which direction I came from).

I realize I am reviving an old thread here but I am experiencing this very same issue on my Vitodens 100W (model B1HA). When I attempt to adjust the set point, it only recognizes and saves certain temperatures and not necessarily the temperature I want. For example, just recently I selected 67 as the set point, hit OK, then when I went back to look at the set point temperature again the display shows 66 as the current temp.

I'm not sure if a resolution was ever determined for this so I wanted to bump this conversation back to the present day.

GGross

lanem2494 said:

pbrisbin said:

3- Can't set some temperatures

This is as simple as it sounds. I literally cannot set the room temperature to certain temperatures. If I move the dial to 60F and press OK, when I go back and look it's back to 61F. It seems to require odd temperatures. If I move it to 58F, press OK, when I go back and look it's shifted to 59F. Same thing happens with reduced room temp. At higher temperatures, it seems to want evens. If I move it to 67F and press OK, when I look again it's shifted to 66F or 68F (depending on which direction I came from).

I realize I am reviving an old thread here but I am experiencing this very same issue on my Vitodens 100W (model B1HA). When I attempt to adjust the set point, it only recognizes and saves certain temperatures and not necessarily the temperature I want. For example, just recently I selected 67 as the set point, hit OK, then when I went back to look at the set point temperature again the display shows 66 as the current temp.

I'm not sure if a resolution was ever determined for this so I wanted to bump this conversation back to the present day.

See if you can set it to 68. It's strange I never encountered this in the field as I sell a ton of these, but I usually don't adjust the room setpoint too much. I am thinking this has to do with the unit being programmed in Celsius but displaying in Fahrenheit. 66f is 18.8889 Celsius 67f is 19.4444c they both round closest to 19c which is closer to 66f try setting it to 68 just to see if it allows that adjustment (that should be the default setting)

lanem2494

I just adjusted the set point to 68 and it is staying at 68. I think you may have cracked the case on this.

GGross

lanem2494 said:

I just adjusted the set point to 68 and it is staying at 68. I think you may have cracked the case on this.

It's a bit confusing for sure. Everything in the programming is based on what they use in Germany, the display just displays the appropriate values for the US market. Confused me the first time I saw the date written out in the backend of the boiler coding. Even though we had it set to display dates the way we do it here the boiler still held the date internally with the European formatting. If you were to get into the deeper coding levels on one of these boilers it displays temperatures in celsius as well, no matter how you have the boiler set to display temperature

lanem2494

I appreciate the info and it makes total sense, but is the set point I chose actually the value the system is using and not the set point that is being displayed? Just wondering if I should overshoot or undershoot by a degree to compensate for the difference in F and C.

GGross

The system doesn't use Fahrenheit at all, so when you select 66f or 67f it chooses the closest temperature in Celsius, which is 19, and displays the closest value in Fahrenheit which is 66, I'm not sure there is a way to see if the system is basing its calculations on a fraction of a degree Celsius or not, if you were to look in the programming it would show a value of 19 Celsius in my experience with no room for fractions of degrees, but that could just be a display thing and not what the computer is using. Typically I leave the room temp setting at 68 and adjust the curve accordingly to meet my needs, whether the thermostat is set to 68, or 72. Depending on your model the "room temperature" setting will also affect your warm weather shutdown, so setting that temperature too low will cause the system to stop heating at a lower outdoor temperature. I generally tell the owner or installer not to set it below 65 or above 72 without first adjusting the heating curve.