Evohome + Opentherm + Viessmann Vitodens 100

[Stulin]

Hi,

Sorry to hi-jack this thread. I have the 100-W B1KC model and the R8810A OpenTherm bridge.

I'm unsure of how these two are wired together. The 100-W wiring manual shows connection ports numbered 1&2 as the OpenTherm communication. Would I be right to assume this is what the R8810A should be connected to?

My electrical, after reading the R8810A install guidance, believes a intermediate control box is required between the two as the R8810A guidance wiring diagram refers to connection ports 7&8 on a board with a reference of W6560C.

Thanks,

Stuart

[Richard]

The Honeywell R8810A OpenTherm Bridge is very easy to wire, as it is just 2 wires that attach to the boiler.

If you contact Viessmann UK Technical Department, they will tell you what to do with regards to their product.

[delahan]

Hello,
I was thinking to get a Viessmann Boiler with Evohome and OpenTherm. Not so sure any more...
Could you please confirm if you are also using the Viessmann OT expansion module https://www.avforums.com/attachments/op ... f.1017128/ and it is not working as required in spite of it?

Thank you.

[a62vw]

The evohome with the R8810A OpenTherm bridge will connect directly to the appropriate terminals on 050 and 100 series boilers without the need for any interface box. The box in the attached link is for controls that provide 0-10v input, which is not Opentherm.

[Stulin]

I just came across this thread, and having a Vitodens 100 connected with an OpenTherm wireless bridge to to evohome, I thought I'd share my experiences:
- yes, the boiler goes up to 81 - 82 degrees and that value can not be changed on the boiler (afaik),
- I also reduced the maximum heating input (as per manual) because the power of the boiler seemed too high. It does work. This makes heating up the house slower, which I appreciate in combination with the adaptive heat up - the floor and walls are warmer when I get home. And by reducing the power, the boiler runs in the condensing range of temperatures for longer periods of time.
- Reducing the power of the boiler also reduced some of the overshoot issues that I have with certain rooms.

Bart,

Thanks for sharing your experiences.

Can I ask, as the boiler is running at the max flow temp range in normal usage, does this have a adverse effect on boiler wear?

I have recently had a Vitodens 100 and the R8810A relay connected and notice when there is no call for heat in any zones, after all zones reach target, the boiler goes into condensing mode with the pump running and does not seem to turn off. As the system has newly been commissioned I haven't had a chance to fully observe the system (the property is not occupied at this time) so is this behaviour by design (OpenTherm) and Evohome (learning mode) and will the pump eventually switch off in time?

[Bart]

The boiler does use different flow temperatures as per demand over OpenTherm, you just can not limit the max flow temperature using the boiler controls, it is hardcoded in the boiler at around 80 degrees exit temperature.
I don't know if it would harm the boiler, but I would not worry about it too much, as it is a limit set by Viesmann themselves.
And again, I find that limiting the flame power does reduce the time that is runs at the maximum temperature.

I can see in my setup that OpenTherm, at least on the Viesmann, does have the tendency to keep the pump running even if the boiler does not seem to burn for some time. If you search this forum I believe you will find some recommendations by the evohome shop such as adding bypass valve or having one (towel) radiator that is always open to keep a minimum flow in the system.

[Stulin]

The boiler does use different flow temperatures as per demand over OpenTherm, you just can not limit the max flow temperature using the boiler controls, it is hardcoded in the boiler at around 80 degrees exit temperature.
I don't know if it would harm the boiler, but I would not worry about it too much, as it is a limit set by Viesmann themselves.
And again, I find that limiting the flame power does reduce the time that is runs at the maximum temperature.

I can see in my setup that OpenTherm, at least on the Viesmann, does have the tendency to keep the pump running even if the boiler does not seem to burn for some time. If you search this forum I believe you will find some recommendations by the evohome shop such as adding bypass valve or having one (towel) radiator that is always open to keep a minimum flow in the system.

Bart,

That is great, thanks for easing my concerns.

I have a bypass on my system anyway and two radiators have dumb TRVs so I should be ok for allowing a constant flow on the system.

Stuart

[schernev]

Hi,
does anyone know about working fix for Viesmann 100 series to work with EvoHome via opentherm.
I bought Viesmann 111W and EvoHome and the guy that will connect evohome told me about this issue and that I need to change the OpenTherm relay to on/off because of there overshoot problems.
I wanted the OpenTherm, but it looks like it is not usable this way...

[Richard]

Unfortunately the solution is to fit a better OpenTherm boiler like an Intergas boiler - https://theintergasshop.co.uk/

Not sure why people go for Viessmann, as Intergas is in a league of its own when it comes to OpenTherm capability...

[Bart]

Probably not many people consider OpenTherm compatibility issues when buying a boiler. Or they are not advised very well.
In my case, the Viessmann was already installed when I bought the house. Nevertheless, it does it's job, even through OpenTherm.