Can a Viessmann weather compensator be overidden/turned off?

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Hello,

We have a Viessmann Vitodens 100 boiler with a weather compensator attached. We have noticed recently, particularly since clocks gone forward, that in the evening the rads in our house are lukewarm, even though the temperature outside is freezing. The outdoor sensor is on a north-west wall, which in the evening gets a lot of sun. I am guessing that the heat from the sun inaccurately makes the sensor think its warmer than it actually is, warming the house accordingly (I sort of have a vague idea about these things work). When the sun goes down, the rads burst into life with a veritable crescendo of heat, by which time we have already gone to bed...

This normally isn't much of a problem but at the moment my wife and I are made up with cold and flu and we just cannot get the house, particularly the living room warm enough. We are sat in the evening literally dithering in the cold. The living room is the worst because it is on the other side of the house, getting only a few hours of sunshine in the morning and that's it. Is there any way of overriding it whenever we want or even switiching it off completely. Now is not the time to be thinking about lower energy bills!!!

I am also assuming maybe WCs are suited for north/south facing houses, rather than east/west. Had we known about this, maybe we would have thought twice about WC, though we did get it at substantial discount with the installation...

It obviously works, but if we cannot override, is there anything else we can do?

Thanks
 
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The outdoor sensor is on a north-west wall, which in the evening gets a lot of sun.

Should be on a north facing wall, so it is never in direct sunlight and measures the air temperature. I knew an installation in which the outside sensor was in direct sunlight in some seasons and then indicated temperatures above 35 degC.

If you don't have a suitable north wall, you can get a reflective radiant heat shroud for the outside sensor, e.g., TT-332 here. You'd need one compatible with your Viessmann controller.

http://www.sontay.com/products/temperature/temperature-sensors-and-pockets
 
Not touched a nerve with me Dan_Robinson... no idea where your post is or what moderator 10 or 11 is... Only just found time to come online.

I had wondered re the moderator 11 post whether I maybe had posted an inappropriate post. I am not sure whether this forum is for trade ppl in the trade, or if, as I believed, it was also for ppl who have no idea about such things seeking advice from ppl in the trade.

I did however briefly saw your post yesterday afternoon. Thanks for advice. I looked in the instruction for installers and found a page to callibrate the compensator by moving the rad control switch up to maximum (apparently this is set to operate the WC). It has made a slight difference but today is a lot warmer so the house is not so bad.

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No, not you at fault
Mods
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Glad you got an improvement Ashley.... its Veissmann who's nerve I seem to have touched. Strange as they are on my list of boiler installation options ;)
 
The heat sensor already looks like this...

Can you move it then, to a North wall or under the eaves where it won't be heated by direct sunlight? There aren't any heat sources near it (flue, extract fan, etc.)?

You could fabricate a baffle in front of it, with a reflective outer surface and some insulation, to minimize the effects of direct sunlight, but the adjacent wall will still heat the air and give an unrepresentative value. It should only be gaining or losing heat to the air, so it indicates the air temperature, with a bit of a lag. If it's in direct sunlight, the sensor is only indicating its own temperature, with which is of no interest.
 

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