Sharky 775 heat meter questions

I’m surprised by this @Zarch.

There ought to be no air being pulled down from the AAV / expansion sessen into that flow sensor now.

Are you fully purged of air in the DHW primary? With pump running air will be “entrained” at certain flowrates and ony “escapes” when the water stops. It can take quite a few start/stop cycles for air to purge.

Do you have a high enough static fill pressure to avoid cavitation? You want to be at least 1 bar on the heat meter flow sensor after system dP is taken into account. (a static fill pressure of 1.5 bar should do it; 2 bar probably won’t hurt)

To be clar though the meter is NOT presenting crazy high numbers to emonCMS here. EmonCMS is reading the WRONG registers from the meter (err-value rather than inst-value) when the fault occurs. There aren’t any instantaneous flowrates reported when the flow sensor is in an error state.

Thanks Marko, really appreciate the feedback.

I’ve been and released/closed the AAV each day, i’ve not noticed much in there aside from the first day or so.

Here’s a capture from last night.
And this is only at around 65% max flow rate
It always seems to get annoyed around 50C flow at the moment.

I will double check the pressure when I get home later.
I have a feeling i’m probably less than 1.5 bar.

Hello Mick, Marco,

Should we be able to recover a reading that will be sufficiently accurate even when it is in error state? sorry I meant to look into this and am happy to do this

Hi Trystan,

The telegram content on the 775 is dynamic. The content of the telgram changes depending on what is available from the meter.

Registers of type “inst-value” are real values. Temperatures/flowrates.

Registers of type “err-value” are error codes. They should not be treated/imported as temperatures/flowrates but were included for some legacy head end systems that would use extreme values for flow/temeprature to signal an error.

Other meters do this in different ways.

Kamstrup meters for example have a static telegram then “info codes” to let you know the meter state. These are also not without quirks. You need to know that “inst-vlaue” of “0” for flowrate doesnt’ actually mean zero flowrate UNLESS the info-code says all is ok. If the info-code says there’s a problem then the “inst-value” for flowrate could be total nonsense.

The Diehl approach of not providing an answer if you don’t know the answer is the safe one; but “column counter” type parsers that don’t include full M-Bus decoding will get confused by them and import the wrong registers when the meters are in error state.

I am genuinely fascinated by this. (sorry, I am a saddo)

What size is the meter? If I have one in the same size (a 775) I’ll post it you for a swap out to rule out the meter.

Where is the install? If I’m passing I wouldn’t mind prodding it in person to try and understand what is happening here.

I have not come across this before but it does seem curiously repeatable!

Looks like it was running around 1.2 bar overnight (and last few months) and i’ve just raised it to 2.0.

As surprised and annoyed as I am!! :rofl:

Nothing wrong with being a saddo / geek!! :+1:

Sharky 775 Heat & Cooling Meter. 3/4" BSP qp 2.5m3/hr.
On a 5kW Vaillant Arotherm setup.

Thanks for the offer, but I’ve already got a Sontex sat here that I got from Trystan & Glyn.

My plan is to give up on the Sharky and try the Sontex.
There is no way I could get Damon back for a fifth time to tweak/mess with the Sharky and be disappointed again.


Sounds absolutely typical for me that this is a one off… only me!!! :exploding_head: :woozy_face:


The first two hot water runs after upping the mbar system pressure to 2.0 and leaving flow rate at 65% max worked okay.

I thought we had cracked it. :rofl:

NO. Upped the flow rate to 100% max and and crapped out again.
(remember, I can run the heating at 700+ flow rate no bother)

I think it’s goodbye Sharky, hello Sontex time!!!



I do have some 2.5 m3/hr Sharky meters here and would happily post you one FOC to rule out your specific meter. Not passing Sheffield any time soon to offer a free installation though I’m afraid.

I do still suspect air in system; and the error codes given by the meter would confirm it if they were logged. Completely understand the “I’ve had it” decision though.

In heating the air would be “entrained” in the pipework, shot into the radiators, and shoot up into the tops of the radiators before the water returned clean.

In hot water there may just be enough air in that loop (or plate) that it gets “entrained” at high flowrates and because it’s “entrained” it isn’t popping up to the top of that pipe stub and into the AAV whilst the water is running.

Enough cycles might clear it (pump flat out; switch repeatedly betwen heating and hot water; in order to flush the entrained air into the rads) but if you do find a Sontex relatively insensitive to air then that’ll also resolve.

You might want to try that. Avoids opening up the system at all. Is there a de-aeration cycle on your heat pump controller that you can use?

LOL Marko, that’s shame you’re not passing, it would have been good to have a saddo chat about it all. :rofl:

Thanks again for replying. Appreciate it.

So, we’ve swapped over to the Sontex 789 yesterday. We’ve placed it in the same location as the outgoing Sharky 775, so a straightforward swap out and hopefully all pipe work / bends sufficient.

I got some strange readings into emoncms over mbus from the get go, ie strange flow rate readings (high), but i’m going to put all this down to air in the system.

I don’t think I can judge the Sontex until i’ve got all the air out as you say Marko. That seems to the be goal.

Interesting side note: The Sontex just seems to give wild high flow rates (like 4.5 m3^h, rather than erroring like the Sharky did). These high flow rates then presented as high power outputs (and as such, higher cop).

heat out = flow rate x dt x SHC after all.

So if the flow rate is being reported wrong (high), the internal heat output calc will be high too. And because electric in is still low (heat output / elec in = cop), the cop looks crazy high, like 15 COP!!

Thinking back over the 7 months of having the heat pump and the Sharky, we have made lots of continual changes to the rad system in the house. Had the bathroom done and made internal rad upgrades in rooms as we’ve gone along.

So never really had a long period where the system has been truly static (and air free?).

So will spend the next few days bleeding rads and checking the system AAV.

Although with the warmer weather now, doubt the heating will be on much and the Eddi / surplus PV is doing most of our hot water! :+1: :partying_face:

Not that i’m aware of on my 5kW Vaillant Arotherm Plus. :man_shrugging:

Any other tips from anyone to de-aerate would be welcome.

I just want a working heat meter setup… I do feel there is something not right somewhere though. It seems very odd that i’m the only person having all these issues, which must point to something about my setup? :frowning_face:

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I can assure you that you are not the only person having these issues.

We see it all the damn time on bespoke / ad hoc heat meter installations for heat pumps.

Also on the upper floors of high rise buildings (cavitation due to insufficient static pressure) or on all floors of high rise buildings where some numpty has designed in “un-bleedable” design details.

With billing bureaus and ESCos happily billing punters based on what are effectively fictional reads. The ESCOs in particular are losing out on a fortune by not recovering ££s for all the heat actually supplied. Hey ho.

Vaillant boilers definitely have built in purge cycles. Arotherms do too I believe:
Installer level → Test menu → Check programmes → P.06 Purge building circuit

You need circulator running and the diverter valve winding betwene positions to purge air into radiators; with pauses for entrained air to settle out. Compressor does not need to be on.

Fascinating that the Sontex unit doesn’t trip out on air. I guess it doesn’t know the difference between collapsing air bubbles and vortices being shed.

Your setup is unusual in having a plate heat exchanger I guess. Most will have coil-in-cylinder that has fewer places for air to hide (tends to rise to the top of the coil naturally; whereas the top of the plate HX is actually between the plates and below the level of the outlet. I assume that all AAVs (including that one atop the plate HC) are open for purging and not stuck shut?


Air can be free (a bubble at the top of a pipe/vessel), dissolved (in the water), or entrained (mixed with the water)

The amount of air that can be dissolved in water decreases with temperature and increases with pressure.

Heat the water and the dissolved air becomes entrained air. Entrained air will trip the flow sensor into an error state.

Entrained air doesn’t rise to the top of a vessel like free air. The only place entrained air becomes free air will be in radiators etc. Or in the (hot) coil of a hot water circuit when the heating cycle there stops. If there’s a coil with an appropriately placed auto-air vent this ought to (in time) purge the free air that un-dissolves as the water temperature rises, becomes entrained due to the water pumping around and around, then has an opportunity to rise up and out somewhere once the system flow stops.

Higher static fill pressures will mitigate / delay the onset of the symptoms.

If logic served I think a lower static fill pressure (and really cooking the water) will be more helpful for this purging process. (big district systems use vacuum degassers for this; these will eventually clear air pockets by dissolving them into the water then sucking that dissolved air out)

Then jacking up the static fill pressure.

Without an auto venting opportunity the only thing you can do is try to entrain the air and send it off out to the radiators (where it can become free air, and then rise to the top, and be let out before it gets cold again and becomes dissolved air) by alternating between heating and hot water mode with the system nice and red hot. Unlikely to be popular at this time of year!


oooooh, isn’t this topic a can of worms and one where arguments start? :rofl:

I’ve been opening the two AAV to release air periodically and then shutting them again.

Because I’d been told that I don’t want to give the opportunity for air to get into the system and affect water quality.

So open the AAV when commissioning / purging and then shutting off when happy?

Is that not right? :man_shrugging:

I think you’ll need to do quite the bit more purging yet either way!

Not getting carried away just yet, but this is promising.

It has been a few weeks since the Sontex went in to replace the Sharky, but i’ve not done too many hot water runs using the Arotherm cos there has been so much surplus sunshine the Eddi PV diverter has done most of the water heating.

Over last few weeks i’ve been gradually upping the DHW flow rate and reached 100% yesterday.

Here’s the graph from last night.

945 flow rate and no recording issues.

I’ve had the AAV open the last 2 weeks and wonder when I should close that off?


So over 6 weeks since I swapped the Sharky 775 out for the Sontex 789 and zero issues reported.

Granted, no heating during that time and hot water runs have been sporadic due to an amazing Solar PV month providing tons of free energy via the Eddi.

I closed the AAV a few weeks ago and occasionally open it up to release any trapped air.

Here’s another hot water run at 100% DHW pump speed.

PS, anyone wanna buy a Sharky? :rofl:


@James314 did your Sharky 775 eventually settle down once the air worked out of your system?

I’m looking at options for low resistance meters for 11.2kW heat pumps and the 1" 775 6m3 is one I’m considering.

@johncantor did you ever re-visit the Qalcosonic E3? The 3.5m3 version looks like another potential option with very low resistance and good value.

If anyone else has one of these meters fitted I’d be keen to hear your experiences.

Hi James. No, i gave up with Qalcosonic. it was odd. faultless on heating, but when it went to DHW and rose above 45C it seemed to go off. I tried a better air separator, but that didn’t help. I then fitted a Sontex and its working fine. I never found out why the Qalco was problematic

Sadly, this was my journey with the Sharky too (as detailed in this thread).

Fine on heating even at max flow rate, problematic on DHW unless I dropped the flow rate below 60% of max.

Replaced with a Sontex and had no issues since.

Dissolved air un-dissolving as water temperature increases and the pressure drops locally within the flow sensor.

If air does dissolve out of all detect this and err on the side of caution by not recording energy use. (which is what you want in the application these are designed for - heating bills)

Install on the flow and ensure decent static fill pressure to mitigate the effect of local pressure drop. Better still deaerate the system by getting it stinking hot and flushing the air through to radiators to be purged whilst hot.

We have these (actually the composite body E4, and in the 6m3 rated version with the same body size as the 3.5m3 rated E3) on a few heat pumps. All but one without issue. That one with issues is on the return and on a system installed with an outdoor plant room and generally impossible to bleed and full of air. It’s slowly getting better as the air is repeatedly bled from rads.

Yes it seems to be OK.

I’ve finally got things logging this weekend. Hot water run looks OK.

Note we have 2 parallel tanks heating - the ‘blip’ in the middle is where the secondary tank reaches temperature and its thermostat closes its flow valve, leaving only the larger primary tank to finish heating.