I’ve never seen this during heating. The only time my flows go towards 60C is during hot water runs.
Which mode have you got the heating set to?
Today was on Expanded because I misread the different descriptions. However I saw 60C target temp at 2C on Inactive. Which is what I will revert to. Speaking to my installer I cleaned out my filter and my flow rate is at 1900l/h again. I suspect this may have been the cause.
My installer has checked with Vaillant and advised me to remove the temperature sensor that is in my buffer. I just pulled out the VF1 connection to the interface. Seems in line with the recommendation run without a buffer. Vaillant have just changed their advice on this apparently.
Had the odd day at COP of 4.5-5.0 in Feb, just bringing down the heat curve has got me to a COP of 3.5 for Feb. Since I’ve been looking at HW and Heating separately I’ve seen a COP between 2.3-2.9 on HW and 3.4-6.6 on Heating.
Hopefully the temp sensor removal will get me to SCOP territory of 4.0. Looks like thats where the break even point for a gas boiler will be next winter going off Cornwall Insights unit price predictions.
My first look at “Normal” versus “Balance” for hot water
Reminder.
So in summary. Not much difference in COP?
Electric input drops in Balance mode for that 2nd half of the run, but so does the heat output, so it would take longer, for not much COP gain?
I’m targeting 55C water here. In Balance mode the water heats to 60C (sticking to DT5). but in Normal it goes to 63C and closer to DT7ish
So that plate seems to be an issue for me when comparing to folks that just have a cylinder with a coil.
I’d be keen to compare in more detail coil versus plate.
I find this interesting,
What causes this profile (the sudden drop)?
This is the beginning of the hot water cycle, when the valve switches from CH circuit to DHW circuit. The water in the cylinder’s coil (or plate heat exchange) is much colder than the water in the heating circuit, so the temperature plummets. Quite normal from what I’ve seen. Some more examples / explanations in this thread:
Interesting. I had a similar issue with my boiler dumping a slug of cold water into the tank on startup. It completely buggered the stratification and made the water heatup even slower.
I solved it by fitting a mixing/dump valve close to the tank that forced the cold flow to circulate back through the boiler until the flow reached a minimum temperature, when it then was allowed to feed the tank.
@Zarch - do you have any Tank sensors to show what is happening there?
The Mixergy shows the bottom of the tank (ie the cold part) is 8C at that stage.
So that probably mixes with the 27C flow/return to create that dip.
The plate heat exchange will also have cold on one side and likely cool water in the other until the diverter flips over?
Timely post, having got my overall COP sorted I’m nagging my installer about HW. I’ve got 73C at the end of my lunch cycle today with target of 54C. Compressor ends up at 65.9% but Power remains on Max. To be honest as you’ve indicated I don’t think the settings will give you much difference in either efficency or power consumption for the difference in time to heat.
Suspect its the Conf. DHW build. pump set to 100. This is where some definitions in the manual would help! Its either a misnamed parameter or needs explaining!
After playing about with various fixed pump speeds on the DHW side, I’ve had it stuck back on Auto for the last month or so.
I get same behaviour in Auto. Am awaiting a response from my installer, who to be fair since I’ve started throwing screenshots and questions at him on email has come back with resolutions.
Any chance you were doing your legionella run at the time? Even though the documentation says it should heat to 60ºC once and then keep it at >=60ºC for an hour, it actually heats it to 70ºC… 
My installer called Vaillant about this and they confirmed that this is normal. Looks like a bug in their documentation.
70C is an overkill for Legionella
60C is sufficient, this can be reduced to 40C-50C if the tank gets a high turnover. You’ll get a higher COP by reducing your DHW max temp to 60C
I’d love to. But I can’t. Vaillant does not make this configurable.
I also do not know my average daily turnover unfortunately.
My 190 liter tank (uniTOWER) is configured to 45ºC with 5º hysteresis. Based on your diagram, I think I’ll:
It definitely is destroying efficiency. That’s crystal clear.
Heat batteries are quite commonly used, their main advantage is they take up less space than DHW tanks. The main manufacturer is https://sunamp.com. @Zapaman has a Sunamp heat battery with his ASHP.
The main disadvantage with heat batteries is there are a bit more expensive than DHW tanks and require a higher flow temp to recharge than a DHW tank, so they will result in slightly lower heat pump COP. However, this may somewhat negated by the lower thermal storage losses.
Heat batteries are a great solution for flats or apartments where space is limited.
Nope, haven’t done a legionella run for about 6 months now. I should really go back to my installer to speak to the Vaillant guru.
In other news I got an esera pcb that I’m going to hook up to the interface to see what I can pull from that. I’ve also jumped onto the Octopus Agile tariff so will play about with home assistant to see if I get that integrated with the Octopus API and Vaillant either through the SensoApp or the PCB. With the Agile tariff and some automation that will make my bills 50% or less compared to a boiler.
I’ve got an SMA Home Manager 2.0, which talks to Vaillant heat pumps via EEBus. When there is sufficient PV surplus, it heats the tank an extra 5°C.
Per the above, my default target is 48°C. Today surplus PV heated it to 53°C.
This was a few hours later:
EDIT: 99% solar heated:
I am still looking for an installer for a heat pump who will install a direct system without hydraulic separation.
The latest visited last week and he seems to be good but is saying that he thinks there is need for a buffer tank and a separate circulation pump as the Vaillant heat pumps do not have powerful enough circulation pumps for a retrofit. He is saying they are really designed for new builds.
This seems odd to me as most of their business must be retrofits.
Should I be looking at a different heat pump manufacturer with better circulation pumps?
Any advice?
Almost every Arotherm on the heatpumpmonitor chart is a retrofit
Now there ‘could’ be a valid reason to separate and have a secondary pump.
But you’d only come to this decision after doing all the calcs and the measurements.
I think the aim should always be no buffer, no separation unless the calcs say otherwise.
It seems like many installers just skip the calcs and default to separation to cover their backsides or cos they don’t understand why they shouldn’t?
Where in the UK are you? Any joy from the heat geek map?
