Evohome + Opentherm + Viessmann Vitodens 100

[Richard]

After a number of years of ignoring the problem of my radiators being set to max / off by the boiler and opentherm, I’m wondering if going back to the simple on/off boiler control via a BDR91 would be better? This was my original plan as the boiler was installed by the previous owner and has an external temperature sensor connected.

The only reason I chose opentherm was that it was easier to wire up. I did physics at school so understand basic wiring diagrams, but couldn’t work out where to wire in the direct on/off wiring from the BDR91.

Can anyone give me some advice on this?

Thanks

Jon

Just wire A and B into the OpenTherm terminal. When the OpenTherm terminal is 'bridged out', the boiler goes for heating demand. When it is 'open circuit' it ceases heating demand. Ideal heating use this exact method for controlling the heating demand for their Logic boilers.

[JustinPW]

First post apologies if already been covered. But noting the original date this thread started it was when the older style of the 100-w was out
Does the problem of the temps still running at 80deg still exist on the latest models ? I have just purchased the B1KF model and have the evohome already fitted to my current old boiler with the BDR91 as the demand switch. With Opentherm being on the new boiler I have ordered the evohome bridge. But will send it back and just stick with the current set up if I can not run with Opentherm at lower temps to maximise condensing mode.
So is it sorted or am I best to save £130 and stick with the BDR91 I have ?

[sidler]

I know this is an old thread but can anyone shared the code and files with me too.
Would love to get opentherm and home assistant working correctly.

[sidler]

First post apologies if already been covered. But noting the original date this thread started it was when the older style of the 100-w was out
Does the problem of the temps still running at 80deg still exist on the latest models ? I have just purchased the B1KF model and have the evohome already fitted to my current old boiler with the BDR91 as the demand switch. With Opentherm being on the new boiler I have ordered the evohome bridge. But will send it back and just stick with the current set up if I can not run with Opentherm at lower temps to maximise condensing mode.
So is it sorted or am I best to save £130 and stick with the BDR91 I have ?

Have a look at this thread. Looks like you will be good to go. I unfortunately have the old model

http://www.ultimatehandyman.co.uk/forum ... p?t=104458

[Ben565]

First post apologies if already been covered. But noting the original date this thread started it was when the older style of the 100-w was out
Does the problem of the temps still running at 80deg still exist on the latest models ? I have just purchased the B1KF model and have the evohome already fitted to my current old boiler with the BDR91 as the demand switch. With Opentherm being on the new boiler I have ordered the evohome bridge. But will send it back and just stick with the current set up if I can not run with Opentherm at lower temps to maximise condensing mode.
So is it sorted or am I best to save £130 and stick with the BDR91 I have ?

Have a look at this thread. Looks like you will be good to go. I unfortunately have the old model

http://www.ultimatehandyman.co.uk/forum ... p?t=104458

aside from the link, can anyone here confirm the B1KF model allowed the max flow temp to be set when using opentherm ?

**EDIT**
I asked Viessmann UK Technical support about setting the maximum flow temperature when OpenTherm is used. Specifically if this was now possible with the new 2021 B1KF version f the Vitodens-100W this was their response.

"Ok, Yes, this has not changed, Any opentherm device when connected to a Viessmann Boiler takes full control and modulation of the boiler, the Panel is redundant from that point on as any settings then have to be performed at the opentherm device settings screen. "

[Jos_T]

Hello everyone,

I recently (February 2023) had a Viessmann Vitodens 100-W B1KF-19kW installed at home. I'm using Evohome in combination with the OpenTherm R8810 boiler module. It seems to work just fine as far as room temperature control is concerned. I was browsing this forum because I'm having some problems with the sanitary warm water controls which are not accessible via the boiler panel. According to Viessmann Support, these controls are taken over by the OpenTherm system. It appears that these functions have not been implemented in Evohome, so it's impossible to switch off/on sanitary warm water. Luckily the hot water setpoint is still accessible via the boiler panel.
Adding to the recent posts on this topic, I don't think that the 80°C flow temperature limit is still an issue nowadays. At least, I haven't noticed it (yet) on my system. I did notice the effect of the OpenTherm modulation control because in steady state the burner was still working but at a very low gas flow rate and low inlet temperature (well below 56 °C at which condensation falls short). I don't know how it was with previous versions of the 100-W but there are 2 parameters in the system configuration that may deal with the problem that was described earlier. The first one is parameter b.2.1, labelled 'Set flow temperature for external demand'. The standard value is 70 °C but it is adjustable from 20 to 82 °C. The other one is b.2.8, 'Maximum flow temperature limit, heating circuit 1'. It is set to 74 °C but is adjustable.
Coming back to my initial sanitary warm water problem: Viessmann told me that the controls can be made accessible on the panel again but it requires a software modification which is something they can do. I haven't decided yet...