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.

[heinzbean]

Crankyman

I read that Opentherm takes care of the flow temps. I manually set my flow temp on the boiler to 55 degrees.

Also i was going to fit an external temp compensation sensor . but realised the Wiser App already has this included. The Opentherm works super efficient for me ...The boiler is nearly always  in eco-mode .House nice an warm and gas bill Half it was previously....

[Crankyman]

Hi Heinzbean,

Opentherm should take care of the flow temperature, so you shouldn't be able to manually set your flow temp to 55?  I certainly can't on mine, if I select the radiator temp on the boiler control panel it won't let me adjust anything, I can of course set the hot water temp Ok. Is your boiler hard wired for opentherm or just how you've set it in the app?

My issue is similar to Hanwellr, that initial turn on when the flow temp spikes to 80, presumably to warm the house up quickly, but I find the hot radiators overpowering, and I don't think it's necessary most of the time as it's rarely below freezing in the UK. After a while the flow temp starts to come down and as you say it then runs nicely in eco-mode.

The wiser app doesn't work in the same way for weather compensation, (I should've said weather and not temperature compensation in my previous post), if you add an external sensor to the boiler it will control the flow temp according to the outside temperature and not necessarily take in to consideration any internal temperature settings.  I believe it's supposed to be very efficient and economical, it's not a straight line from boiler off at say 20 outside to 55 at 5 outside but a curve programmed into the boiler, of which there are several you can choose from to get a comfortable inside temp, at least that's my understanding from the boiler manual. This Viessmann brochure explains it much better than I can

I keep threatening to buy the sensor and try it, but I haven't done yet!

[hanwellr]

Thanks for the update yes geting simlar feed back from the app. One thing I did notice in Home assistant I have the wiser feeding back and notice there is no value for the return temp. 

What I have done outside of this is build ESP32 temp sensor and have one on the flow and return pipe. 

[Lactophobe]

From Viessmann...

Weather compensation or Open therm can only be used individually it would only be a case of using one or the other