Sharky 775 heat meter questions

Hello everyone.

I will shortly be having an Arotherm+ ASHP (7kW) installed onto a new system and want to get monitoring kit ready. I already have some SDM120 meters and can talk to them with Python.

I’m looking at the Sharky 775 (2.5m3 nominal flow) from Stockshed with MBus module, which looks like it has acceptable pressure (head) loss at max ASHP flow and seems to be one of the most accurate meters.

Before I press the button on it, does anyone have any wise words on this meter, and also is there any other kit required to install it, like extra sensor pockets (which Stockshed do sell) or any pipework adapters? It seems to be for 22mm pipe but I expect our main ASHP feeds will be in 28mm even though they will be short.

Many thanks in advance.

Great stuff, you can read directly from the SDM120s via emonHub to get the data straight into Emoncms & MQTT:

We usually use Sontex or Kamstrup heat meters in our ASHP monitoring bundle, however emonHub can also read from Sharkey. The 2.5m3 is a good choice, I’m assuming you’ve seen our choosing a heat meter page?

As confirmed by @Zarch the default Sharkey MBUS ID is 25 therefore the following config will work:

    Type = EmonHubMBUSInterfacer
        device = /dev/ttyAMA0
        baud = 2400
        pubchannels = ToEmonCMS,
        read_interval = 10
        validate_checksum = False
        nodename = mbus
                address = 25
                type = standard

You will need a couple of 3/4" female BSP to 28mm compression irons e.g Brass Compression 28mm x 3/4 inch Straight Adaptor Female CxFi

and a 1/2" female 28mm compression branch tee for the temperature sensor pocket on the flow, the heat meter will fit on the return e.g Compression Female Branch Tee 28mm x28mm x 1/2"

Many thanks Glyn. Yes I was using your guide to choosing a heat meter (very useful!).

Any reason you prefer the Sontex and Kamstrup meters? I could always choose one of those if there is a good reason to, though the Sharky seems well priced and with good accuracy.

Hi James

I went for the Sharky as it seemed to hit the value angle for both MBUS and mains powered.
The equivalent 22mm Kamstrup was almost £100 more and the Sontex 749/789 don’t seem to have a mains feed? Although there is a note that it can take some power from the MBUS line?

Not sure I’d trust any other meter as they aren’t on the open energy / John Cantor ‘approved’ list.

Anyway, i’m just flagging up i’m having a few issues with the Sharky and it monitoring flow rate now i’ve got my 5kW Vaillant Arotherm up and running.

On my hot water runs, the flow rate goes towards 0.9m3/h it just flips out and reports back a crazy high figure. Like 131 m3/h!!! :woozy_face:

I can prove the issue by turning down the max pump output to 75% and the Sharky happily records around 0.7 m3/h. But turn it back up to 80% + or to Auto and it flips out.

The issue makes no sense as the 22mm version is rated to 2.5m3/h and the Vaillant screen is only reporting a max of around 1.0 m3/h.

I’m running the hot water via plate heat exchanger into the Mixergy tank. But I can’t see that being an issue?

I’ve reported my findings back to StockShed and hopefully they will come back with an answer. Maybe i’ve got a faulty unit.

As flow rate is critical to getting accurate heat output and COP it needs to be right.

This issue might not happen to you. But just thought i’d let you know.

Thanks Mick that’s useful info, it does sound strange. Is it always when it hits the same flow rate, or hits the same water temp?

Searching the forum it looks like @richardsmith99 has a Sharky 775 - Richard, any similar issues?

I had some error issues with it that came back to air in the system causing errors. It seemed to get trapped in the HW coil so ran happily on heating mode but not the water. Eventually everything just worked its way out but it did cause a fair bit of irritation.

The sharky showed an error code (7?) on the screen at the time

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No particular reason, other than familiarity. The Sontex 789 is well priced but has significant pressure drop so only suitable for smaller heat pumps. Supposedly Sontex is able to handle debris and air bubbles in the fluid without effecting the readings. Kamstrup have very low pressure drop.

We do actually have a Sharky in the office which I keep meaning to do some more testing with. It does look like a nice unit with some interesting communication outputs.

Correct, when the battery powered Sontex 749/789 is connected to MBUS it draws its power from the MBUS reader therefore it’s effectively mains powered, I tested this myself by removing the battery!

Interesting, I’m assuming you’ve double-checked there’s no air in the system? Interested to hear what Stockshed say.

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Thanks Richard. I will set off a hot water run and check the screen later.

Did the problem present itself with sky high flow readings?

Hot water run this afternoon. All going well with Sharky matching the flow rate on the Vaillant controller.

Then boom, 25 mins in it went mad.

Error 7 confirmed on the unit.

I’ve got Altecnic auto air vent on the DHW / plate side, so wouldn’t expect any air in there.

The Sharky seems to think otherwise.

Error Code - E7

No plausible ultrasound receiver signal, e.g. air in the measuring path

Then once the DHW cycle had finished, Sharky woke up again and started recording 0.8, 0.7, 0.6 m3/h etc. with no problems.

I will have another chat with my heating engineer. See what they say.

Is it possible to tell the Arotherm to limit the flow rate during a DHW cycle?

Yes, we can do that. You can put max speeds on both heating and DHW independently.

But when the Sharky is faulting at only 0.8m3/h when it’s rated to 2.5m3/h. :man_shrugging:

I’d rather be able to do my hot water rate at full pelt to get the water heated.

I don’t want to constrain my heat pump just cos the heat meter can’t handle it?

I was more wondering if there was a flow rate you could set that meant it completed the DHW cycle and didn’t fault - therefore showing it’s most likely a flow rate effect not temperature?

If it’s not air in the system then I wonder (clutching at straws a bit) if there is some ultrasonic oscillation being set up in the pipework somewhere at higher flows.

Or maybe just a faulty unit as you say.

The hot water cycle does complete fine. The Vaillant just cracks on, with 800l/h showing on the display.
It is only the Sharky that shows the error message.

Error message clears once the DHW run is finished.
But what is strange, is that all the subsequent heating runs are showing 800l/h with no issues… so :man_shrugging:

Me confused.

Have sent all this new info to StockShed.

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This sounds like it could be the culprit. From the Sharky install guide:

They recommend a straight length of 10 DN pipe before the meter i.e 280mm on 28mm pipe. Here’s a photo @Zarch sent me of the heat meter installation there’s an 90 deg elbow directly before the meter. At high flow rates this elbow will be causing turbulence which could be effecting the reading?


Balls. We saw the diagram, hence mounting vertically. Missed the small print.


Will see if we can look at getting that rejigged. :frowning_face:

Do Sontex and Kamstrup also have these requirements?

It looks like it can be horizontal or vertical, just not at the highest point in the system. Hope it’s not too much hassle to fix, at least it looks like you have free space above for a straight bit of pipe?

Damon says it’s nothing some elbows can’t sort out!! :rofl:


Don’t understand why heating engineers don’t use long radius bends where they can to help with flow. I think it is just the cheap 90° are in the bag already.

I was interested that my plumber used all Press fittings when the boiler got replaced. Great innovation.

From my memory it produced some sky high numbers before just crashing to error state and no data until it settled again

We made the pipe work changes and put a really long straight before the meter.

Same problem occurs.

What’s weird is that you can run the heating at the max pump speed (800l/h) and the Sharky works fine.

But you put the hot water run anything about 600 l/h and it craps out.

Perhaps it’s because the DHW run is so short (3m from outside unit, to plate/tank, then back again)?
You can physically here ‘noise’ around the circuit when you ramp up the DHW pump.

So maybe it’s just something I have to live with (lower pump speeds on DHW) if I want the Sharky in place?