Setting Vittodens 200-W to external demand not working, any suggestions?

ChrisMcc

Hello,

I have a Vittodens 200-W with the standard Vitotronic control. I have a Grundfos circulator pump (on connection 20) that runs continuously. The unit has outdoor reset and I have verified that when the outside temperature is above the room set temperature the pump is switched off. However, in any other case the pump is on and it's about 180W.

I looked at the video that Viessman posted about switching to ED and read some docs and all the service manual. I have 3 Taco pump controllers (2 x 506, 1 x 504EXT). I have connected the end of line relays together and verified I get a closed relay when any zone calls for heat. The system also does DHW. In this case it has a LLH and the DHW circulator pump is downstream (system side) of the header. That pump is connected to connection 21 in the Vittodens. This has been running well for years.

I connected the combined, paralleled relays to DE1 input and set location 3A to 2 and location 3F to 2 in the coding. I verified in the information in the menu afterward that it saw EA1 input 1 as demand. I also verified that if I call for heat from any zone the Vittodens is seeing the relay close and is showing it as on in the information.

So, all looks good, at least to me. But the Vittodens still never turns off the ciculator pump. I would expect it to be on if either there was external demand indicated from the pump controllers or if it was heating DHW (since that needs to header and manifold to be supplied in this config) but I would expect it to turn off otherwise.

Have I fundamentally misunderstood this or can anyone perhaps offer any suggestions. Attaching a photo of the Vitotronic in case that's of any help.

Thanks,

Chris

PXL_20230329_170835100.jpg

GGross

Off the top of my head I can't remember which programming codes will control the boiler pump operation. Keep in mind that the "external demand" function that you are enabling eliminates ODR heating curve from the equation and just gives you a set point temp operation, not ideal.

One thing that you can do if you just wish to operate the pump on/off with the thermostat call, and let the boiler still use ODR heating curve, is to wire the pump in as a "boiler pump" on your zone pump relay. So the pump kicks on when any zone calls for heat. This would kind of "trick" the boiler since the pump will only come on when there is a call for heat, the boiler will only fire when there is a call for heat, and you can still use the ODR heating curve, you would need to set your coding values that you changed back to 0 for this to work. The boiler is equipped with a flow switch safety device which famously does not trigger a fault code, so you should end up with a boiler running on ODR that only fires when you give it a call for heat. a bit of extra work for sure lol. The new ones are set up better for the US market, and they did a control update on that style control that allowed for a similar function as well (not worth buying a new control for imo)

ChrisMcc

Thanks, I contemplated something similar. I think it's a little more complex because I have three different zone circulator controllers and it doesn't look lik the two SR 506-4's are set up for this. I also need the boiler pump to come on when it calls for DHW and that's controlled within the Vittodens. I had contemplated using the DHW circulator pump on output 21 to trigger a relay and the end of line switches to trigger a relay and using an OR of the two in order to turn on the boiler pump. I could just add a 120 VAC coil NO relay in parallel with the three existing Taco controller end switch relays and then use that combined NO relay to switch the coil on a relay for the boiler pumpe. But I'm building a lot of control system here. I was hoping there was an easier way to do this.

I'm not sure how useful the outdoor reset really is in our case to be honest. With programmed thermostats it always feels like the thermostats are fighting with the boiler anyways.

I ultimately feel this is worth it. I have a monitor on the overall system and, even in winter, we tend to run <60% of the time calling for any heat or hot water. That's about 1.75KwH/day of energy that doesn't seem like it needs to be used.

ChrisMcc

Also, one question: you mention the flow switch safety. If I understand this correctly (and I may not) this prevents the boiler from actually firing if there's no flow in the system, correct? That would prevent the boiler running when it isn't actually delivering heat. I suppose that and the temperature limit protect in this case.

GGross

Is your system piped similar to this? nevermind the exact number of zone pumps, more concerned with the boiler side of the low loss header

Capture.JPG

ChrisMcc

No it is not. The pump P2 (in that picture) is located alongside pumps P3-P6 (in this picture). So it's on what the manual I have calls the "system side of the LLH." This seems to be covered as an alternate configuration in one of the install manuals I have. This is still coded as a type "2" system and programming code 5B needs to be set to "1" for "DHW tank connected downstream of the low loss header."

GGross

They had made a running change to some programming at one point to allow for an easier change to on/off operation. I know this coding address is also in your boilers control. I believe you can change this in LEVEL1 or 2 coding, should be in GENERAL address 51 change to 1 (default should be 0) with the newer control update this would turn off the pump when there is no heat demand, it will run a bit after burner shutdown for a preset post purge time

I also missed your other question. Yes the flow switch will prevent the burner from firing if the boiler does not detect correct flow, this could be caused by a failed pump, or if the heat exchanger becomes airlocked. It will not give you an error code, however there is a way to see hidden status indicators in the control. Generally though with a Viessmann if it won't fire and gives no error code and should be firing, then the boiler does not detect flow, there are a few exceptions to this with larger model boilers, and if you were to program a DE terminal with EXTERNAL BLOCKING instead of DEMAND it would also shut down the burner with no error code. The last bits are not relevant to you I just add them in case someone happens across this thread in the future

ChrisMcc

Thanks! I'll give that a try and see how it goes.

ChrisMcc

Thank you @GGross ! That worked perfectly. The only slightly odd thing is related to DHW. I verified that if I run some hot water and the DHW loading pump switches on then the heating circulator pump also switches on, just as I need it to. Oddly, in the information section of the menus the circulator pump stays listed as OFF. I have verified that when a zone calls for heat the EA1 DE1 input is listed as supplying demand and the circulator pump shows as ON, and it is, again, ON, so all seems to be working perfectly.

The one thing I'm not clear on is the setting in coding location 9B. This is the boiler temperature with external demand. In this video https://www.bing.com/videos/search?q=vittodens+200-w+external+demand&view=detail&mid=EBAC4F610374E057EDA8EBAC4F610374E057EDA8&FORM=VIRE, they move it to 86C. It defaults to 70C. Do you know if this relates to coding location 6 which is "maximum limit of boiler water temperature"? My location 6 is set to 86C, perhaps coincidentally the same as the value chosen in the video. That's 186F which is really hot, I don't need that with a DHW set point at 122F. I chose 76C for location 9B but I don't know if there's a better way to tune this.

GGross

leave 6 as is, 9B is your setpoint temperature so choose the temperature that works best for your situation. I think in that video they were just showing that you could turn it up all the way to high limit, lower temperature is better so long as it still heats what it needs to