Wiser OpenTherm Setting the Flow Temp on Combi Viessmann

[hanwellr]

Hello,

I have Wiser kit 1 working with Openthem  on a Viessmann Combi. There are no issues and the Combi is set up to take Openthem commands. 

The question is should I alter the maximum flow tempurature from 80 to 60? What i'm wondering is if the Openthem does alter the requested flow temp. Seem each time I ask for a room to be heated the request is going for 100% (80) and never see a request lower? My understanding is that as the room gets to temp then the request should be lower than 100% and there for the flow should be lower?

Wonder if other people just set a lower flow temp at the boiler to get around this. 

[Crankyman · Accepted solution]

I have a Viessmann combi with a kit 1 too.

My flow temp does drop from the initial 80 as the room temperature starts to climb and I've seen flow temps of 35.  I find the initial flow rate of 80 very annoying as I don't believe it's necessary, and a lower flow temp would be more appropriate as radiators at 80 are very hot!

I've tried to lower the maximum flow temperature on the boiler, but as per the opentherm spec, the controller (Wiser HubR) commands the temperature and overrides any changes on the boiler, so I don't think you can lower the flow temp whilst wired for opentherm.

My system works well overall, but I really do hate that initial 10 minutes or so at 80 degrees before the temperature throttles back.

I'm toying with fitting the external temperature sensor and letting the Viessmann control the flow temp according to how cold it is outside (Temperature compensation) and just use the Wiser system to call the heating on and off so it's not running 24/7.  However I'm not sure whether the system would need to run longer at lower flow temperatures, rather than me turning the boiler on and off  using the Wiser system.