The Max Cyl Charging Time is set to 120 mins on the sensoComfort 
Weird. What target temperature have you set?
Set it to 0 and it ignores it.
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The system is all underfloor, ± 100 m^2, open loop in a 1970’s house with moderate insulation improvements. It is running on weather curve 0.3 in adaptive mode, as it is close to the coast with high wind impacts. Heat loss at -3 according to the data is 4.16 kW.
There no volumiser. However, the 20 meter 32 mm MLCP run does sort of work in that way. And is the primary pipework from HP to UFH manifold.
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Of course it does, I will have a play, thank you Mick
50C is the target temperature.
Excellent! So if ’Max Cyl Charging Time’ is set to 0, then the unit will continue to charge the cylinder for as long as it takes to reach the set point temp (within the scheduled DHW times)?
Handy for the winter, when defrost cycles stretch out the DHW cycles…
Yeah. No limits.
I mention it in more details here.
But it does have its pitfalls in eco. Especially with a 5kW unit and a large cylinder as I talk about here.
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I’ve been thinking that there’s two ways we could approach this as there’s only two ways that I can think of that adjust the targetflowtemp
- Adjust the WC curve
- Adjust the target indoor temp
I’m saying this because I don’t think we can directly poke into targetflowtemp?
The curve / indoor target temp combo would just change it back?
I’m torn between which option might be best, so thinking out loud.
I think adjusting the internal target temp might be easier? Especially as we know each 1C internal temp change is about 2.5C target flow.
We’ve also seen that switching from Inactive to Active provides around a 2.5C targetflowtemp adjustment. And i’ve come to the conclusion that 2.5C isn’t usually a strong enough a change
So maybe the script would adjust the target indoor temp by 2C, so causing a 5C shift in targetflowtemp?
ie, set up some rules
- if target indoor temp > (greater than) room temp = drop target indoor temp by 2C (to drive down target flowtemp)
- if target indoor temp < (less than) room temp = increase target indoor temp by 2C (to drive up target flowtemp)
Or something like that?
You could maybe add some granularity to the if statements. if > 1C, if > 2C etc
Lots of thinking out loud there. 
So i’m ignoring the outdoor temp as i’m more concerned about the disparity between indoor temp and the target indoor temp.
And by leaving the WC curve in place, I know that when it’s sub 3C outside, that somewhere around 0.45 to 0.5 works for me.
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Hey Mick. Some interesting information there, do you tend to leave your system on active as opposed to inactive all year around even in the summer?
I seem to go from one and the other, not sure which to settle on. I’ve had two radiators upgraded the other day (bigger ones as that room striggled a tiny bit to get to temp) in the main living room where the sensocomfort is, I’m finding now that the room temp is overshooting compared to the older radiators, granted it’s warm outside now so may have to wait until it’s cold outside to balance the new radiators, they are so much more efficient. I assume the best way to combat this is to play with th HC until it settles on a temp?
Hope I can pick your brains about DHW, I’ve done the sweat spot settings as per your blog post and that’s helpful massively getting my COP up, cheers for the tips. My question is are you planning keeping it at sweat spot all year around or do you move it to fully ECO mode for the warmer summer months to maximise efficiency?
Yes, i’m going to stick with Sweet Spot DHW for two main reasons
- I want to collect a years worth of data so I can compare that to the 700 Eco runs from last year.
- I actually like the hot water being back full in around an hour. We are still a family of four who like showers, so it’s working okay for us.
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So setting Max Cyl Charging time to “off” had no effect, my HW Boost cut off after 61 mins tonight with tank temp about 12C below target. I’ll check with Vaillant…
Maybe it’s really the boost mode. Did you try whether the normal mode has the same issue?
You can mimick the boost mode by just setting the hysteresis to 20°C on the controller and adjusting the target temperature in Home assistant. If you set that to 35°C (lowest possible) when you don’t want anything to be produced. With the 20°C hystersis, the water would have to drop to 15°C to be triggered automatically. When you want hot water, have home assistant set the target temperature to 70°C to definitely trigger a cycle and then set it back to your target. It’s more involved but exactly this setup works for me also with eco and really long cycles.
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The manual DHW ‘Boost’ trigger via the Sensocomfort/app will only run the DHW for 60 minutes, as you are experiencing. This is as per design, and cannot be changed as far as I’m aware.
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I think the compressor starts at 50rps, and EEV is completely open. this means high flow of refrigerant and low pressure difference in refrigerant loop. High flow means, little undercooling in the condensor. Then EEV closes gradually, lowering the refrigerant flow, untill the actual undercooling starts getting close to the targeted undercooling. closing eev means larger pressure difference and temperature after the compressor rises. Now we have a temperature difference between compressor outlet and water return, and a refrigerant flow that is in balance with the power the water can pick up. then it is time to control towards the water flow temparature actually wanted.
This would probably work for my use case.
I like using the Operation state of Cylinder Boost from the integration to assign Energy usage to a consumption sensor.
I really should stop procrastinating and start having a play with the PCB and EBUS connection. I just have a cabling issue to solve which is putting me off.
If you also set the timeout between successive DHW cycles to 0 on the controller, you could just trigger boost a second time if you don’t reach the temperature. Might impact efficiency though due to the extra compressor start and ramp-up.
Hot Water Boost:
My normal DHW target temp is 50, hysteresis is 10, max 90 minute reheat period, and no further reheat for 60 minutes. At the moment it’s scheduled to only reheat between 10pm and midnight, and cylinder is only reheated 3 or 4 times a week due to low hot water use.
I’ve had visitors recently, and naively assumed that Hot Water Boost would do just that - heat the cylinder up to the target temperature on demand to allow a number of showers over a period of several hours. But that doesn’t seem to be the case, and despite some tinkering I haven’t figured out the algorithm used to actually kickstart a DHW cycle.
As well as target tank temperature, what other parameters come into play for the Boost to take effect or not? What’s least amount of temporary reconfiguration when I have a houseful of visitors?
What did the hot water boost do then? It should start a DHW cycle but it runs for max. 1h. When I want to trigger a quick reheat manually I either use a Hone Assistant automation that sets the DHW Target temperature to 70°C for a minute and then back, which triggers a cycle (as long as current temperature<70-Hysteresis). You can also just increase target temp from the Vaillant app for a minute.
Thanks Andre. The boost didn’t seem to do anything!
The first time I tried at about 9 am the tank temperature was showing as 32 degrees. The heating was on but Boost did nothing. I can’t remember what other changes I tried. After about half an hour I turned the heating off altogether (heating mode OFF) and a bit later I heard the DHW cycle start. I then turned heating back ON and DHW cycle continued.
The second attempt was about 2pm a few days later. The tank temperature was 39.5 so outside hysteresis range, but I knew there were potentially two showers planned and a big pile of washing up, and wanted to top up heating during Cosy 1-4pm cheap period, rather than during peak rate 4-7pm. This time I increased target tank temperature to 55, and still nothing happened. Soon after 3pm I cancelled the boost and tried again. Still nothing. I cancelled the boost a second time before 4pm and DHW reheated according to the schedule at 10pm.
In both cases the app appears to show heating, hot water and boost on which is a bit misleading.
I haven’t found anything in the documentation to say that the same constraints apply to a hot water boost as they do to normal DHW - but maybe I just haven’t looked in the right place.
I just tried your 70 degree tip - with the app showing tank temperature to be 35 degrees, I increased the target tank temp to 70 before boosting (and then quickly reset to 50 before I forgot!). That worked perfectly, I heard the diverter click over within a minute, tank was reheated to 50 and heat pump then reverted to space heating. But it might be easier for me to swap from time-controlled to manual while there are visitors staying, and then back to time-controlled again when they leave.
I contacted Vaillant yesterday to ask for guidance on how the Boost functionality works. I’m not expecting anything useful from them but who knows…