2005 Viessmann 100 Boiler and Weather Compensation - help?

31 Oct 2010
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United Kingdom
Hi All,

I have a 2005 Viessmann 100 type 7179916

I recently purchased a Viessmann original weather compensation sensor for use with this boiler. I was told it would come with instructions but it doesn't!

1) Does anyone know how the weather compensation sensor should be connected?
2) How can I properly test that it's working?

Thanks in advance,

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Did somebody tell you that weather compensation works with the older Vitodens 100? :confused: :confused: :confused:
Yes, they did. The guy at Viessmann Spares did - he phoned Viessmann tech support. I'm beginning to wonder if I've been told porkies!

Do we know either way?


As I understand it, the latest 100 does accept Weather Compensation, and Viessmann announced this with a bit of a bang, but the old one didn't

Did you make clear to the supplier your model (WB1A, I presume) and serial no?
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I was never sure about which model it was but I told him the type code. He phoned Viessmann but must not have told them the right thing.

I have now found the installation manual and there's no mention of it there. Must not be supported. Oh well, I was looking forward to having that functionality. I guess I'll be sending the part back! I've opened the packet, so hope that will be ok.


What about OpenTherm? Can I connect a modulating thermostat to the WB1A?

I want to try to avoid the endless cycling of the boiler and the fact that our radiators get very hot and we always seem to be fiddling with the temperature control on the boiler.


Why do you feel the need to keep fiddling with the boiler stat? :confused:

Is it cycling on CH or on HW?

Are your radiators balanced, and do they have TRVs?

What is your cyl stat set to?

Do you mean a programmable thermostat? (sets room temp according to time of day or night)
Hi John,

Thank you. We do have TRVs on all the rads. We don't have a room thermostat.

CH cycles on and off regularly. We set the dial on the front of the boiler to the mark about the 2pm point on the dial. Seems to run the CH water at 60-70 deg C.

In the evenings the boiler runs for half an hour or so then shuts off and then starts again after about 15. This is a problem because all the pipes start clicking as they expand and contract all the time, disturbing children in bed in the evenings.

We always find ourselves turning down the temperature dial for a bit when the house seems to get too hot, then finding the house is cold and going and turning it back up again. Our TRVs are all set at the mark for comfort (can't remember the exact setting) and do appear to be working.


We don't have a room thermostat.
:eek: :cry: :cry: :cry:
You need one.
Your comfort and economy are not achieved without it.
CH cycles on and off regularly. ......We always find ourselves turning down the temperature dial for a bit when the house seems to get too hot, then finding the house is cold and going and turning it back up again. ...
Well it would, because you haven't got a room stat.

You can get a basic one for about a tenner, I recently went over to a programmable stat which might cost you about £40, but I reckon it's worth it. You can also get wireless ones but I am suspicious of these because it gives you one more thing to go wrong.

I have always been very happy with ACL/Drayton controls, part of Invensys, but Honeywell and others are also well-known brands





I am a householder not a pro, but I also have a Vitodens 100.

p.s. On a programmable room stat, "holiday mode" means you can press buttons to say "I am going to be away for nn days, leave the heating at n degrees untl the day before I get back, then go to normal daily routine"
Yes, I always wondered why a room thermostat wasn't installed when our heating engineers designed and specified our system.

I'd been meaning to fit one for some time...

Thank you for the links. I will check them out!

OK - so I called them this morning and they have sent me the instructions!

So here they are for anyone else that needs them:

I must connect the sensor to X3, pin 1 and 2 then set dip switch 2 to "on" (flip down the front of the control panel to access them).

Then the temperature dial on the front of the boiler doesn't directly control the temperature of the CH water. However, the automatically adjusted temperature curve can be altered slightly by moving the dial to warmer or colder as appropriate.

I'll try it over the next few days and report back.


You have a WB1A boiler. It will accept weather compensation. Phone Viessmann Technical tomorrow for details.

As a matter of interest why did Viessmann never admit that W/C could be used on the WB1A until about January 2009 ?

I wonder if they wanted to guide buyers towards the 200?
I doubt it.

It was mostly existing boilers that people were asking about.

Nor am I so sure the 200 was available when the 100 was first sold here.

But you might be right. If so then I think thats rather naughty!

I installed the sensor as suggested, and it's working well. A good result: the boiler turns itself down as the outside temperature increases. The house no longer gets oppressively hot, and the radiators are generally cooler to the touch. The boiler also cycles less.

Thanks all for your comments.


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