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Viessman 100W Outdoor Sensor

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Have a Viessmann 100W B1HA125. I was aware at install that an outdoor temp sensor was installed and wired to boiler for weather compensation. However just recently I looked more into the boiler and realized that the sensor wire was never hooked up to terminals 3&4, wire is just hanging loose inside. Obviously the outdoor temp is not being displayed on the panel as a separate reading in addition to the boiler temp. I want to take advantage of weather compensation to modulate boiler temp, and set the heating curve as per manual. My question is this- the manual says if a sensor is not being used to leave terminals 3&4 not connected to anything. But the installer wired a jumper between the terminals. Any idea why this was done? Maybe this is common practice on a similar boiler?

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  • GGross
    GGross Member Posts: 1,065
    edited February 2023
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    The original B1HA came with a jumper installed on 1&2, to allow for constant operation with weather comp mode. I would double check that this is not the config youhave and maybe the loose wires are Tstat wires left there just in case constant did not work correctly. If the jumper is installed across 3&4 I am not sure why that was done, and not sure how you would not have a fault for a lead break in the outdoor sensor.

    If i remember correctly you can take the terminal strip out of there, so don't rely on it reading 1,2,3,4 from left to right, take it off and look at the numbers
    runningRich
  • runningRich
    runningRich Member Posts: 2
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    Thanks for the tips. It is hard to see the terminal numbers as you said. I have wires 1 & 2 going to my zone controller, per manual.

    The jumper is currently across 3 & 4, but manual states jumper is only used on 1 & 2, and only if room temperature thermostat (optionally via zone controller) is not installed.







    I'm going to remove the jumper 1st and test for normal operation, and if that's the case I'll connect the sensor, see if the outdour temp is then displayed, and set the heating curve.
    GGross
  • GGross
    GGross Member Posts: 1,065
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    Yeah that certainly is strange they put that jumper in. Your current plan should get you going correctly
    runningRich