I wish that heating engineers used a pipe bender. There are still 4 right angles to create flow disturbance. A nice smooth, bent pipe would be sooo much better, but 90° bends as so much simpler.
Very odd.
“You can physically here ‘noise’ around the circuit when you ramp up the DHW pump” - Maybe still some air in the system?
Agh this is a very frustrating problem, I’m not sure what else to suggest other than trying to contact Sharky technical support. I was on the phone with Adrian from Stockshed today, he’s received your email but not had a chance to look at it fully yet. Stockshed are very good, but they are a reseller, I think this is a question for Sharky directly.
Have you got some manual air release valves you can open to see if there’s any remaining air in the system?
As a side note the instructions for my Sika flow sensor that I had to install as part of my Samsung heatpump specify that the sensor should not be installed on a vertical downwards flow because of the increased possibility of air bubbles. I know Sharky don’t mention this, but if there is a bit of air still in the system it’s more likely it will be an issue since the meter is located on the downwards leg.
Kamstrup which uses the same ultrasonic measurement technique as Skarky advise against installed on a downward leg (D) but don’t go as far as prohibiting it:
What pressure is the system at? Sharky don’t see to mention anything about pressure, but Kamstrup specify min 1.5 bar - max 2.5 bar
Thanks Glyn
System is at 1.6 bar
I will drop an email to Sharky themselves, see what they say.
We’ve installed auto air vents in two positions now on the water loop side, one right at the highest point on the photo, just before the Sharky.
Maybe the downward position is the problem?
It’s all pretty frustrating. 
As water is heated dissolved gas will be more likely to come out of solution (pressure and temp dependent)…
I guess in a ‘down’ leg bubbles are working against the flow (they will try and float up) which makes it worse?
Useful info to be aware of, not something I would necesarily have thought too hard about otherwise!
I logged a support call directly with Diehl which went to their German helpdesk.
They punted it over to the UK support desk.
Who were going to get their local support technician to talk to me.
Only to change their mind and suggest I needed to report the issue to Stockshed!!
Agh what a nightmare. Is the meter manageable in its current state? Can you just avoid using higher flow rate? I run my system at 16 L/min, I didn’t notice any drop in performance when I reduced it down from 22 L/min. Assuming the flow rate is sufficient to deliver the required energy, running at a lower flow rate results in less pumping power required, therefore marginally higher COP.
Setting my friends Sharky 775 up.
Out of the box the Pri_add is 59!!
So definitely check the ID on your own unit before setting up.
It sounds like it could be anything out of the box!
On my Kamstrup heat meters, the default Meter-Bus IDs are the last 2 digits of the Serial Number. I notice the close-up of your meter (showing the E7 code) has 25 as the last 2 digits of the number below the barcode, so wondering if Diehl/Sharky follow the same convention. Does your friend’s meter have 59 as the last 2 digits there by any chance?
Yes, I’ve also realised this. A fallback method if you don’t know the ID is to do a MBUS scan using libmbus
sudo apt-get install -y cmake
sudo git clone https://github.com/rscada/libmbus.git
cd libmbus
sudo ./build.sh
sudo make install
cd bin
sudo ln -s /usr/local/lib/libmbus.so.0 /usr/lib/libmbus.so.0
./mbus-serial-scan -d -b 2400 /dev/ttyUSB0
Yes, that’s true. We use this script which can be used to set the Kamstrup ID, default to 1
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oooh, that’s a good spot, I will check when I go back and confirm.
Although it is pretty straightforward to cycle to menu 3 and see the pri_addr setting on the unit. 
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Some info here that could be transferred to the docs?
Confirmed. I remembered I’d taken a photo of my mates Sharky and the serial sticker on the front does indeed end 59.
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So whilst my heating guy Damon was here this week I had him move the Sharky for the THIRD time.
So we are now flat, with DN10 before and DN5 after as per the Sharky docs.
Guess what? It’s WORSE now than it was on the downward section.\
I’m all for giving up on this Sharky, I really am.
We had over 1000lph (16lpm) in heating mode yesterday, it was fine recorded with no issues.
But as soon as the hot water kicks in, even at just 700lph it craps out, errors and throws rubbish data to my emoncms and screwing up heat output data. It’s proper frustrating!!
My historical data is no ruined with a daily COP of 52.3!!!
Last thing I can see in the Sharky manual to try is…
We also urgently recommend installing the flow sensor in a tilted position (45°) in
order to remove possible air bubbles from the circuit.
After that, i’m out of suggestions apart from buy a Sontex?
I’ve heard nothing back from StockShed or Sharky themselves on this. That’s been poor too!!
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If you paid by credit card, I’d try for a refund under Section 75; not fit for purpose.
[edit]
Either it is faulty or this is what it always does and no one takes that much notice of the data!
I have a question on this, powering a Sontex via MBUS.
Will it increase the power draw on the Raspberry Pi 3?
I’m already running a heatpump HAT as well as the Modbus USB interface for the SDM.
When using the 5V DC power adapter from the shop, i’ve occasionally seen under voltage messages in dmesg.
Had an update from Diehl (via Stock Shed)
It could be great to install the flow sensor in a titled position (45°), it’s often the problem when we see E7.
Please let me know if it solves the issue.
I’ve resigned myself to buying a Sontex and installing that, but I suppose I best try this for completeness. 
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I may be tempting fate but after much deliberation I’ve bought a 6m3/h (1" BSP thread) sharky 775.
Should be OK for the flow rates we’ll see with our HP (also checked with Stockshed) even though they are on the lower end of its rating. It also has really low pressure drop and matches the 28mm primaries.
Our system is being installed the week of the 20th so will report back on how it goes…!
Meanwhile it’s interesting that this larger unit does not have a tap for a temp sensor in the brass body - so you need 2 half inch tees one for each temp sensor…
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That’s interesting, where did you hear this? The photo of the large body seems to show a pocket for a sensor:
