Opentherm + EvoHome + Viessmann 111-W overshoots

[StephenC]

Indeed, you're right Paul. Got caught up in the technicalities for a bit there.

I guess that's why having the BDR91 there and available so I can run that most of the time, and then if time permits and I get a chance to look at external OT device control options, I can switch the R8810 back in to test.

I'm not sure I'll gain a lot on money by selling the R8810, so as DBMandrake said, maybe hang on to the R8810 OT Bridge in case either EvoHome is updated with a feature, or I build/buy a OT override device.

Is it possible have both heat trigger devices (switched live and Opentherm) connected to a boiler?

I'm guessing I'd need a physical switch on one of the R8810 OT wires to short it out if I wanted BDR91 Relay control thinking about it.

[StephenC]

I've just re-read the following thread around Lyric T6 and Ideal boiler with Opentherm.

Situation seems familiar. Are we at a point do we think that the UK boiler manufacturers are actively trying to avoid correct and working Opentherm interoperability? There are now a number of people on this forum who have interoperability issues - with Honeywell and boiler manufacturer both saying the other is at fault (actually I feel Honeywell are in the clear from what I can see so far)

http://www.wordpress-1219309-4387497.cloudwaysapps.com/vbulletin/showthread.php?4996-Ideal-Vogue-amp-Opentherm-via-Honeywell-T6-Lyric-(wired-version)&highlight=Lyric

Also, the Opentherm "DIY monitor/override controller" tip has been mentioned a few times by a few people. I wonder if there is demand for a few people on here working together on this? I guess I'm saying I don't feel this is at present something I can do on my own as I don't have coding or electrical component assembly experience, but I'd be happy to purchase a fairly finished kit, assist, be a tester, provide feedback etc. Maybe someone with and R8810 Opentherm Bridge, coding and electronic component assembly skills (or rather experience) is willing to lead?

[bruce_miranda]

And I don't think the HR92s will ever learn to cope with 80+C flow temperatures. I am fairly convinced that the system using a rolling 7 day average. Rather than develop long term memory.

[bruce_miranda]

And it is possible to run 240V switched live and OT. I was running my boiler in this configuration until I worked out how to get the OT bridge to fire my boiler. But I suspect in your case, even if this was possible the simple presence of the OT bridge on the bus will render your CH max flow knob useless. So I don't know what you will gain.

[paulockenden]

The most shocking aspect of this, as I'm concerned, is how Veissmann (or rather, their uk distributor) has handled this.

I'd always thought of them as a premium band. "The Rolls Royce" of boilers. That illusion is now well and truly shattered.

[bruce_miranda]

Indeed and when you think about how easily they can fix this. Just issue instructions to upgrade the firmware on the boiler to treat the OT max command as optional, as per the OT specifications. It almost looks like they designed their own OT interface backwards from the CM737! Ignoring all the other OT devices that assume certain defaults.

[StephenC]

In section 5.2 it clearly states that 25 Boiler temperature is Not mandatory. So why is your boiler expecting the OT bridge to set one?

Hi Bruce,

just had a quick look at the Opentherm spec once again, and I think you've mistaken OT ID 25 (Boiler flow water sensor temperature (°C)) for OT ID 57 (Max CH water setpoint (°C))

i.e.

ID 25 is informational sensor data from slave (boiler) back to master (controller)
ID57 is configuration target data from master (controller) to slave (boiler)




From re-reading the spec, it looks that it is optional for the slave (boiler) to send through ID 57 to the master (controller or R8810 OT Bridge in our case). I'm guessing maybe the Viessmann doesn't send anything, and therefore R8810 OT Bridge requests its default max CH flow temp of 90 degrees C . This is then actually capped at approx 81/82 degrees C on a Viessmann boiler through some kind of limiter function maybe.


These are part of:

Section 5.3.5 Class 5 : Pre-Defined Remote Boiler Parameters - page 27


Does this change your view on the omission of max CH flow temp configuration ability on EvoHome? (I'm not saying Viessmann have done a sterling job here by the way....just trying to establish facts before engaging Viessmann in Germany)

Stephen

[bruce_miranda]

None of the other boilers that work with OT need the Evohome to set the max, so why is Viessmann needing it. I suspect the only reason it does is because Viessmann have assumed that the OT device that is plugged in will have configurable parameters, the Evohome doesn't.

[StephenC]

I've finally had a response from Viessmann international to my email regarding the issues I'm having.


They have now confirmed in writing and admitted the issues I am and also other are seeing are the same as their setup.


Interestingly, the reply was from the UK Tech support team:


"Dear Sir,

Thank you for your recent enquiry.

Following your initial enquiry, we have looked into the issue and can advise that when an opentherm device is connected into our boiler opentherm connections then it takes over full control of the boiler, the controls on the front of the boiler are overidden as you correctly identified in the US manual. Weather Compensation is also disabled so would not give functional control back if fitted.

If a switch live option is available on the Honeywell controller and is connected to our switch live connections on the boiler, then the controls on the front of the boiler can be used, however, we do not know what affect this will have on the functionality of the Honeywell controller. The communication protocol used by the Honeywell controls are unknown to us, therefore, we cannot comment or advise on how it will actually control / modulate our boiler.

We trust this clarifies your enquiry.

Kind Regards
Lee Pedley
Technical Supervisor
Viessmann Ltd
Hortonwood 30
Telford TF1 7YP"



Does this imply "just connecting" the BDR91 Relay to the switched live connections whilst leaving R8810 Opentherm Bridge in place and connected may allow the ch flow temp dial to start working again, solving the issue? I'll not bind the evotouch controller to the BDR91.

Maybe this is a workaround. I'm waiting for the Gas Safe engineer to have the BDR91 connected back up again anyway, so may ask to experiment.

[bruce_miranda]

Switched Live is just on and off. The boiler will still listen to OT to set the target temp, which is actually your issue. The boiler will only hand back control when there is no OT on the bus.

[paulockenden]

The communication protocol used by the Honeywell controls are unknown to us

Says the company selling a (supposedly) Opentherm compatible boiler.

Jeez...

[bruce_miranda]

I wonder what will happen if you point out that we know that the OT control sold by them is made by Honeywell!

[StephenC]

Yes, you're right, just reread their email. I was jumping on nothing there....

Anyway, I guess that is case closed on this now.

I'm heading back to BDR91 (+ Weather comp now) asap when I can get hold of my Gas Safe Engineer.

I can't say I'll be buying a Viessmann again. That said, it's only 2 years old, so I don't want a new boiler just yet!

Thanks all for the advice on this.

[bruce_miranda]

Maybe if you made your feelings more publicly known they might do something. It's a few lines of code after all, not like swapping out the heat exchanger

[paulockenden]

Such a shame because they seem to be well made boilers. I wonder whether it's just the UK distributor being clueless, and whether 'back home' they are more clued up on the subject?

Have you had any contact with the German techies?

P.