Hi everybody,
I would very much appreciate your help in identifying whether the following is normal behavior or whether something can be improved; apologies for the English version, my knowledge of German language is nil.
I have an underfloor heating system and the following equipment: Vitodens 200W B2H 32kW (2020/2021, 7 inch color display), Vitocell W100 (200l) – in front of the low loss header, low loss header (ZK03679), 3 way switching valve with electric drive (mixer) and external Grundfos Magna 1 pump for the heating circuit, EM-EA1 extension (in order to ensure command of the boiler from all zones/room thermostats/three separate distributors - the automation in each distributor is linked to the extension - in DI1/2/3, and standard /comfort/reduced temperatures are all identical in the boiler setup) and EM-MX for the mixer; whether controlled, temperature sensors in the low loss header and after Magna 1 on the flow output. Operating mode of heating is "off" - as it starts only upon requests for heating from the room thermostats.
After preparation of hot water, the internal pump runs for the time set up in the setup menu (not less than 120s), and then stops. When it stops, if there is a heating request from any of the zones, the external pump starts (it is off during the hot water preparation phase). Depending on the flow temperature in the underfloor circuit the burner starts or not. Eventually, as the water in the underfloor circuit is circulated, its temperature decreases and the burner starts – but it stops very quickly, as the water temperature in the heating supply rises sharply, because its temperature is high (after hot water preparation, and it does not decrease while the external pump runs).
I have managed to get to a couple of burner starts per day (for heating) but every time hot water is prepared there is this “failed” start – afterwards it works OK, the temperature of the water in the heating supply now decreases (while the internal pump is still off, only with the external pump running) – it’s like the 3 way diverter valve only switches to the heating position and hence letting the water through the low loss header only after a request for heating exists and not at the end of the hot water heating phase. (by the way, what is its implicit position – hot water or heating?)
Various values for differential temperature in the low loss header make no difference – currently at 0. Neither is the value of the integral threshold for burner switch-off. Internal pump speed during hot water preparation -100%, while for heating it is at around 80-90% (and fixed, as per the manual, don’t know the value by heart); heating power is limited for both hot water preparation and heating.
To me it looks like the 3 way diverter valve / internal pump management could be (maybe?) better – or maybe I have missed some settings. I imagine that my setup is quite common - I would then expect to be able to avoid these "false" burner starts...
Any thoughts you may have are appreciated and thank you for your time reading this.
All the best!
