Vitodens 111-W DHW Control

[Tom Shea]

Good afternoon all,

Apologies for going around the buoy again on an already discussed topic.

I have a Viessmann Vitodens 111-W boiler, Honeywell Evohome with BDR91 relay and HR91 TRVs. I work away from home and currently the only control that I have over the DHW is to turn it off at the boiler whenever I’m away.

I have the hot water kit but now have the issue that I think that I will need the OpenTherm Controller to be able to utilise this.

My future intention is to use OpenTherm but would prefer to not have to shell out post Christmas, is there a way to control the DHW without? I have read through the thread regarding 111-W overshoot and seen a number of recommendations to return to BDR91 but can’t see where on the electrical connections it could/should go.

I will also be getting the OpenTherm Gateway to address the overshooting issue but again would prefer some time to raise funds.

Thank you in advance.

Tom

[bruce_miranda]

If the Viessmann Vitodens 111-W boiler's HW can be controlled using an external programmer, then it can be controlled using a relay. So does it? If all you want is app control of that HW switch then just stick a Wemo or Alexa plug on it - job done.

[Tom Shea]

Unfortunately the only electrical connections in terms of control are through F connection (controlling CH and currently being initiated by BDR91) and the OpenTherm connection. I think that the Viessmann controllers use OpenTherm to monitor the DHW and maintain temperature/schedule. (Attached diagram).

I’ve seen people on previous posts talk about reverting back to BDR91 as a result of OpenTherm overshoot so didn’t know if there was a way of controlling DHW that I couldn’t see. The DHW cylinder is powered by the same circuit as the rest of the boiler therefore no possibility of isolating it and using a controllable socket.

[sandyman]

looking at that boilers datasheet, seems to me its a storage combi?
Install manual P97 covers how the storage cylinder is controlled:

Heating the DHW loading cylinder from cold
The heating circuit pump is switched ON and the 3-
way diverter valve will be changed over, if the cylinder
temperature sensor captures a temperature lower than
the defaulted set value.
■ The cylinder loading pump is switched ON if the
boiler water temperature ≥ set cylinder temperature.
■ The burner is switched ON if the boiler water temperature ≤ set cylinder temperature, and the cylinder
loading pump is switched ON when the required
boiler water temperature is reached.
The loading cylinder is heated up to the set cylinder
temperature. Heating stops when the specified temperature has been reached at the cylinder temperature
sensor.
Reheating when DHW is drawn off
When DHW is drawn off, cold water enters the lower
section of the loading cylinder.
The heating circuit pump is switched ON and the 3-
way diverter valve is changed over, if the cylinder temperature sensor captures a temperature lower than the
defaulted set value.
■ The cylinder loading pump is switched ON if the
boiler water temperature ≥ set cylinder temperature.
■ The burner is switched ON if the boiler water temperature ≤ set cylinder temperature, and the cylinder
loading pump is switched ON when the required
boiler water temperature is reached.

which makes perfect sense - the controls for these are internal to the boiler. looking at the electricals, in the manual on Page 99
S - terminal block X5 terminals 3 and 4 - cylinder temp sensor
O - terminal block X9 terminals 1 through 6 - diverter valve motor controls

so theoretically I suspect you could tap into those terminals and put in external switching / control of your own making . However, warranty would be likely be dubious in this situation - I wouldn't do it.
looks like the opentherm controller for this device is for heating control only.

what hot water kit do you mean? I have one for my heat-only viessman but I don't see how that applies to a storage combi?