Same here - I have a Sharky (another ultrasonic flow sensor) and it settled down after a little while once the air worked its way out of the system.
Dissolved air in your system.
Raise the fill pressure; get it good and hot; bleed the radiators; switch back and forth from DHW to purge the water with disoolved air from the DHW loop; bleed the radiators etc.
Once there isn’t air in the flow sensor it will work correctly.
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I ended up adding a Spirovent deaerator/air separator just after the heat pump primary flow comes inside - I got bored of waiting for the air to work it’s way out via the radiators or existing automatic vents. After a while the issue went away for me too.
Is the flow going vertical, upwards through the meter? From the emonHP user guide (taken from Kamstrup install guide)
Position B (upwards flow) is fine, but position D (downwards flow) is suboptimal. Either should be fine once all the water is purged from the system.
The flow meter is in position D, 30cm down from the T bringing the feeds back together for the return to the heat pump, and 20cm above a manual isolator valve. The pipework is 22mm OD copper, so should be just about good enough. It’s running at a pressure of 1.75bar.
There is a deaerator in the system and I have bleed all the radiators over the last few days. Initially some air did come out but now nothing.
The net result has been a slightly improvement in the flow measurement during the DHW cycle (the flow measurement doesn’t crash straight away), but it is still far from fixed.
Any further ideas or do I need to get the installer to move?
Could you post photos of the installation? Try increasing pressure to 2 bar and keep bleeding radiators and ensure automatic air valves are open. It usually takes a few weeks for all the air to be purged from a system. Small pockets of air gets trapped inside the DHW coil.
Here’s another photo showing the complete indoor installation (yes, it’s a tight squeeze and the cabling is a bit of a mess right now as I have added lots of digital thermometers to emon on the radiator side of the buffer tank and elsewhere in order to better understand what is going on!).
I’ve now increased to pressure to 2bar, and have bleed the radiators again (no air is now coming out).
Here’s hoping I can get a clean flow measurement.
Mixergy tank?
Using a coil or a plate? Air loves to hide in plates. Any means of bleeding it other than hoping to flush into the rads over time?
I’d try bleeding from that pressure relief valve. That’ll trap some air given th orientation. Also from the magnaclean whilst it’s in hot water mode and stinking hot. What’s the lump of brass to the right?
Is that an auto air vent on a buffer in the foreground? Working correctly?
I’d have fitted the heat meter flowrate sensor on the supply not the return myself. Higher dynamic pressure there and less likely to cavitate.
Using a coil or a plate? Air loves to hide in plates. Any means of bleeding it other than hoping to flush into the rads over time?
It’s the Mixergy plate heat exchanger. I can’t see any way of bleeding in but the installer is back later in the week and I’ll get him to check.
I’d try bleeding from that pressure relief valve. That’ll trap some air given th orientation. Also from the magnaclean whilst it’s in hot water mode and stinking hot. What’s the lump of brass to the right?
I’ll try these as well. The lump of brass is a Spirovent deaerator. Not sure how to tell if it’s working.
Is that an auto air vent on a buffer in the foreground? Working correctly?
Yes, according to the manual that came with the buffer tank, it’s an auto air vent on the top. Interestingly, I hadn’t looked at the buffer tank manual before and I cans see that it has a holder for a temperature sensor. As I have a spare 1 on my EmonPi I’ll install it. As a separate exercise I’m trying to understand the heat flows involved with the buffer tank.
I guess the installer fitted in the return loop because of space constraints. I am thinking of asking them to move it to my loft space the other side of the wall where the pipes are easily accessible and straight. I’ll see what progress I make before they come.
Ask the installer to show you the little cabps and fibre washers on the top of the spiro / air vents and how to use those
Thanks for everyone’s help. My flow readings have much improved during the DHW heating cycle. As you can see below, I am now getting readings throughout the whole period although there is still some turbulence at the higher feed temperatures. This was achieved by further bleeding of the system, especially the Mixergy heat exchanger and other “high points”. I’ll monitor it to see if there is further improvement.
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