I've now had a written response to the email I sent to Viessmann last week. My previous notes in this thread relating to Viessmann, were phone calls to be clear.
Once again (@Rameses), Viessmann are stating this is a Honeywell issue as the R8810 should not be locking out the onboard boiler controls:
"If the Honeywell control worked fine whilst using the switch live demand through the BDR91 then there is no logical reason why, when connected to the open therm through a R8810 Bridge, this should be any different, the boiler control logic should not be overridden by the Evohome, If the boiler is set to 65 degrees for example then the Evohome should not force the boiler to 81/82 degrees.
We suggest you ask Honeywell if any settings can be made to the Evohome to adjust this issue, potentially, if the boiler is being forced to 82 degrees this is very close to the boiler limit stat and could potentially cause the boiler to lock out and no heating would be available until the boiler is reset.
All of our boilers are fully modulating and have had open therm connection for the past 10 years without any issue.
Kind Regards
Lee Pedley
Viessmann Technical Support"
I still think it's odd that there are 2 users in this thread with a locked out ch flow temp dial, and also the US manual for very similar Viessmann combi boiler explicitly states the control will be locked out..who is right? Hopefully in time we'll find out.
Once again (@Rameses), Viessmann are stating this is a Honeywell issue as the R8810 should not be locking out the onboard boiler controls:
"If the Honeywell control worked fine whilst using the switch live demand through the BDR91 then there is no logical reason why, when connected to the open therm through a R8810 Bridge, this should be any different, the boiler control logic should not be overridden by the Evohome, If the boiler is set to 65 degrees for example then the Evohome should not force the boiler to 81/82 degrees.
We suggest you ask Honeywell if any settings can be made to the Evohome to adjust this issue, potentially, if the boiler is being forced to 82 degrees this is very close to the boiler limit stat and could potentially cause the boiler to lock out and no heating would be available until the boiler is reset.
All of our boilers are fully modulating and have had open therm connection for the past 10 years without any issue.
Kind Regards
Lee Pedley
Viessmann Technical Support"
I still think it's odd that there are 2 users in this thread with a locked out ch flow temp dial, and also the US manual for very similar Viessmann combi boiler explicitly states the control will be locked out..who is right? Hopefully in time we'll find out.
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