Google nest / Viessman combi storage boiler / opentherm question

[MassiveJim]

As per title I am using a Viessman Vitodens 111w combi storage boiler with a google nest thermostat connected using opentherm.

there seems to be a delay when hot water is initially called for, before the thermostat kicks in and calls for heat, presumably this is controlled/triggered by the temperature of the built in storage tank (around 40l iirc)

what this means normally is halfway through a shower I get a bit of a drop in temperature, where the storage tank has been fully used and the boiler cant keep up with the demand + trying to top the storage tank back up at the same time.

I recently had Veissman out to look at the boiler and I mentioned this problem to the engineer, he pressed a button on the nest transmitter which put the boiler into manual mode and it calls for water immediately when you turn on a hot water tap in this mode.

If I go into the next controller and disable the hot water element of the controller, it doesn't actually change the hot water side to manual as i would like, and it prevents me from being able to change the settings for hot water on the boiler itself (for example the temperature)

i know these boilers aren't super common so I'm probably stretching here to ask if anyone else has a similar issue or even better a solution

 

[MassiveJim]

noone?

 

[ianmcd]

If I go into the next controller and disable the hot water element of the controller, it doesn't actually change the hot water side to manual

It wont , set the HW shedule on the Nest to constantly on

 

[MassiveJim]

It wont , set the HW shedule on the Nest to constantly on

there is no schedule, and it is set to "on" as that is the only setting.

 

[ianmcd]

have you installed your nest as dual channel ? it should bet installed with only the heating terminals connected , the HW is controlled by the boiler not the nest