Auto is not max, Auto is 50% my side, I had to manually adjust it to get my desired flow rate ( to 75% for me )
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But auto is also not consistently 50% - at 50% my heat pump turns off because it does not reach minimum flow. What’s your max.rem.head setting?
good question ! it was my next thought ,
About the Head setting in mBar, how do we know the value to set ? only thanks to calculation on the pressure losses or is there a way to “see” the good setting ?
I’ve set it to 600 by guessing …
I honestly have no clue. I’m using it to control pump speed, as it has a better granularity than the percentages of pump speed. I have it at 450 mBar, which translates to 1100 liter/hour flow rate with the pump on auto (minimum for my heat pump).
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Yes, pump speed is on auto.
Remaining feed head is at max of 900mbar.
Flow rate currently at 13.7l/m
Just spotted that installers left room temp at 22, so flow temp higher than expected. Have changed it back to 19.5.
What happens when you manually set the pump to 100% instead of auto?
Thanks @Andre_K. I am working with the installer on this, so won’t change the pump speed at the moment. Just asking in case anyone else has had a similar problem, identified the cause and then fixed the problem!
The installer is planning to flush the plate heat exchanger in the heat pump next, since the gradual reduction in flow rate is symptomatic of debris in the system. If that makes no difference then he is likely to call Vaillant out.
I will pass on your suggestion to change the pump from auto to 100%, although I don’t quite understand why - will that help clear any partial blockages somewhere in the system?
The installer did run a ‘purge building circuit’ cycle before leaving on Monday, and I thought I remembered him saying last summer that runs pump at full power. After the purge there was a slight increase in flow rate, but it started dropping immediately.
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Setting the pump to 100% won’t clear debris, it’s just to see what flow rate you’re getting. But I totally agreey gradual decrease of flow indicates some form of blockage. It looks like your installer is on top of things for now and hopefully can resolve your issues with the flush. Let us know how it goes.
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Hopefully each individual radator will also be flush from the heatpump connection while all other radators are closed, so the full force of the flushing unit is concentrated on each piperun in turn. (Radiator needs to be fully open, so will need a complete rebalance after flushing.)
That could simply be down to poor system design, where the flow is restricted by either radiators or UFH valves not allowing enough flow, or the pipework being too small (15mm rather than 22mm for the main flow and returns for zones
I think in this case flow rate was fine at some point and degraded over time, which is most likely not due to poor design
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Or maybe it was never noticed until it really started to manifest itself in the system performance 
Sometime flow rate looks OK due to unbalanced radiators, but system can’t cope if radiators are correctly balanced.
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That’s a good point. Would that essentially mean one or a few radiators are “stealing” all the flow when unbalanced but upon balancing the other radiators don’t receive that flow due to high resistance in the pipes towards those radiators?
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Don’t there’s an issue with the design. Main flow and returns all 22mm. Some plastic pipework on ground floor only discovered when radiators upgraded. This was replaced with copper when problems with flow rate, and from then on flow rate ok. Small amount of plastic pipwork on 1st floor remains. That was a joint decision.
@Ringi and @Andre_K
Radiator balancing might or might not be relevant in this case.
They were balanced temprarily in October for the house as it is was then. Ground floor is partly uncovered - long story, I’m mostly living upstairs, and we got the upstairs rooms to a reasonably even temperature, apart from loft bedroom, where radiator was upgraded on Monday, from K2 1600x600 to K2 2000x700.
After the flow rate had already started reducing, and my bedroom became uncomfortably cold in early January, I ramped up heat curve from 0.65 to 0.7, and also opened up my bedroom radiator lockshield by 1 (from 0.5 to 1.5) and closed down another bedroom by same amount (from 5.5 to 4.5). Flow rate continued its steady descent.
And as of this week I have a bigger radiator in the loft bedroom, and flow rate is still going down steadily, but from a slightly higher starting point.
I don’t fully understand the concept of resistance in the pipes yet I’m afraid. I need to find a nice easy explainer 
Everything has been a huge learning curve this last 12 months…
0.5 to 1.5 and 5.5 to 4.5 sounds like settings on the TRV’s.
Balancing is done with a spanner on the LOCKSHIELD valve - the opposite end to the TRV. The cap is frequently screwed on to discourage adjustment
I know it might seem like that but I have IMI bi-directional thermostatic radiator valves and lockshield on all radiators.
I set this one to 5.5 - see the little slot in the nut between the 5 and the 6.
The installer can also view my Home Assistant data so he could see which rooms were too hot and which too cold. Last October he was doing the lockshield calculations at home, then telling me what adjustments to make (in the range 0.5 to 8.5). We had 3 rounds of adjustments I think. Doing it like this saved him travel time, and definitely helped me learn a bit more!
As I said, all the TRVs are open at the moment. Next spring when the heating is still on but I’m getting more solar gain from the low sun into south facing rooms, we’ll use the TRVs to cap the temperature in those rooms.
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To follow up, I changed the target temp down to 43 degrees, which resulted in a flow temp of 47 and tank temp of 43. Then back up to 48 degrees which resulted in a flow temp of 52 degrees and cylinder temp of 48 degrees. E.g. all fine, the 60+ degree runs just seem to be a glitch in the matrix…
I have also had a play about with the cylinder charging offset and as you say, it seems to have no bearing on the flow temp actually achieved!
A couple of follow on questions for interest:
- What is the typical dT people are getting across the coil in their cylinders? For me it’s typically ~2.5 degrees.
- What duty do people have the circulation pump set to for DHW? Mine was set to ECO + Auto but a Vaillant engineer came round a while ago and changed it (without asking) to Normal + 100%. I changed back to Eco but left pump at 100%. Wondering whether to stick it back on auto…
For me it’s 3.3K with flow rate on 100% and eco.