Accuracy of Outdoor Reset Temp Sensor for Viessmann Vitodens B1KE-120 Combi
I had a Viessmann Vitodens B1KE-120 Combi installed about 9 months ago and I've recently noticed that the temperature reported by the "external temperature sensor" according to the ViCare app reads about 9 degrees warmer than the actual temperature.
According to the local weather report and my kitchen probe it's about 49 degrees F outside right now, but the external temp sensor of my Viessmann says it's 58 degrees. I've noticed this for the past few weeks as the weather has gotten colder.
The sensor is mounted on the exterior wall that is adjacent to the boiler closet.
Am I missing something? Should I ask the installer to fix under warranty?
I realize it's probably not a big deal because I can just compensate via the level and slope of the heating curve, but I'm also kind of annoyed that it's so off.
Comments
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Is it on the north side of the building? Is it out of the direct sunlight?
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You can set a correction for the measured outdoor temp in the boiler control. page 61 of the install manual to start
896.0 “Display correction for outside temperature”
-10k to +10k default is zero, each increment is 1.8f
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It seems most inaccurate overnight. Around midnight I saw a similar error amount, maybe even a bit more. But currently around 10am the sensor says 51.8 and the forecast says 52
The sensor is under a covered patio that faces roughly north-east
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That's good to know. The problem is that it seems most inaccurate overnight. The issues I noticed were around midnight but currently around 10am the sensor says 51.8 and the forecast says 52. So it appears to sometimes be accurate.
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If I had to wager a guess the sensor is accurate, it is just sometimes a different temperature at the sensor location than the forecast temp. Figuring out why is the important bit, the best way to check would be to read the value the sensor is actively reading when you think it is off (with a meter at the terminals), make sure the value matches what the boiler temp says, and then to back it up with a separate temperature reading at the sensor location. the sensor itself is quite simple really and wouldn't just intermittently read incorrectly, but it is possible there is something that is affecting the sensor temperature location. For example if the flue exhaust is hitting the sensor, but only at certain times of day due to various factors that could throw off the sensor. It's reading accurately but external factors are making it incorrect. The colder it gets the more the boiler will run, which could mean the flue gas has more impact on the sensor, it's colder at night. I would make sure the sensor is not being messed with by the flues as an initial check
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@GGross See photos below for location of exterior sensor, how it's routed through wall, and location of flue about 5 feet further into the closet. I also added a photo of the pressure gauge because I wanted to ask if that was ok. Looks like it's around 10 or 12 psi, but a little under the green.
I should do a temp check outside right near the sensor, but I can't imagine it's that different, unless heat from the closet is influencing it. One data point though is my system was entirely off starting at 9pm and these reading were still a problem hours later.
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I'd seal that hole up where the wire exits the building. Heat could be escaping there and warming the sensor from the back.
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Yeah, good idea. Any recommendations for what to use?
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That sensor looks pretty close to the vent grill on that boiler door. I would move it to the other side where it is still in the shade but gets more outside airflow.
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The heat from the house will throw off the sensor especially in a sheltered location.
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foam in a can. But move the sensor out of the covered area.
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The sensor is high in a porch corner where it seems like warmer air would get trapped. I too don't like the looks of those vent louvres nearby and below the sensor.
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I would prefer the static pressure when the system is cold to be about 15 PSI, The expansion tank pressure will need to be adjusted to match the system static pressure, the contractor most likely set it at 12 since that is pretty standard and what most expansion tanks are factory set at.
If you stand back a bit farther can you get more of the install in your picture?
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FYI, that PSI was while the heating system was running, though the water temp was only around 80 F IIRC.
Here's another pic… if you click on it you see the full resolution:
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Given that the boiler is internet connected and knows the local weather, is there a way to change the settings so that it uses the internet sourced temp for the outdoor reset?
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That's a good question, I know they ran into some kind of legal issue with wifi connectivity and some remote features were left off the US models. I haven't done this before but I will check it out
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