Keep getting my Octopus Heat Pump doing the following
Was also getting strange noises one has stopped, another one has replaced it
Site: Emoncms - app view
All was good till a few days ago with the charts
There is air in your primary going through the heat meter again. That is what you are seeing on the DHW reheat cycle.
Guessing that sound should be a radio show phone in where the prize fund increases by £10 each week until somebody gets it right. 
It sounds more like air and water being vented. Is there a pressure relief valve blowing off anywhere? System fill pressure changing? Is your system fill loop connected permanently?
Octopus Energy are the folks that you have paid for the install. They have issued you with an MCS certificate which is supposed to be proof that your installation has been designed, installed & commissioned to the highest standard:
Ask them back to investigate and resolve why the system has air in it and is making odd sounds again? If it is repeatable it should be quick to identify.
I might mention that you are considering hiring an independent expert to take a look at it at their expense if they are not able to solve it on the third attempt. At that point you have given them a fair chance at delivering what they have promised. In any civil claim the judge would be minded take the position that on the balance of probabilities you have let them have a good go at it and they simply aren’t capable of delivering what they have promised in the contract; so it is therefore reasonable to pay somebody else to deliver what was promised in the contract and then demand they pay you for the work needed to finish the job in accordance with the contract.
It would never go to court as they have in house counsel who know when they’re going to lose so would square up with you without all the hassle of going to court.
(this is why those same lawyers wrote the £7500 maximum liability limit into the contract - to limit their losses in the event they promise to deliver something that they cannot)
We have already had Octopus Energy out and I thought they resolved the air trapped issue as it was working perfectly after they left. They even left the house radiators on, though they feel luke warm to the touch, house heated up as day was quite nice then to a toasty 25 degrees when I then set it back to 21 after they left.
So one day temperature dropped below 21 degrees radiators must have kicked in, at which point the charts started to show this annomoly. Octopus only replaced some of the radiators, wondering if the old ratiators need replacing too. I would not think air keep getting trapped like that should keep happening so frequently.
It’s been suggested I bleed the radiators, and top up to 1.5 to 2 bars. It’s at that bar and Octopus already did the following in their last visit
Drained the water from the tank and radiators
Added lots of Sentinel X100 solution to system tank I believe
Repiped a load of pipes added some pressure valves to pipes in cupboard
Replaced the white blow off cylinder in the cupboard (Not the main cylinder)
The filling loop has been left disconnected as they said that’s how it should be left. We have not touched any of it, left it well alone so no idea about valves blowing off, water being vented etc.
Octopus want to replace the heat meter, which they say will fix it. I’m in two minds because I think that may just solve the symptom and not the actual underlining problem if it exists and obviously if their is a issue it needs fixing at the root cause.
If the heating has kicked in since the visit; then all the water that was in those will have been circulated through the system including the heat pump unit and the hot water circuit. Any air that was in that water is now also in the heat pump unit and hot water circuit.
Sentinel X100 does nothing for air.
Personally I would not allow Octopus to “hide the symptoms” by removing your heat meter (which can tell you when there is air in the system) and installing one that can’t tell you if there is air in the system or dirt in the meter. (e.g. a PowaGaz or Zenner branded mechancial meter, or a Sontex branded vortex-shedding meter)
As it stands you have a MID certified measuring instrument that is explicitly telling Octopus that there is air in the system they have installed. Previously it was also telling Octopus that the primary flowrate was too high for the 3-port valve they had used. If they don’t want to fix this and instead want to remove yor only independent eyes and ears on the system they have installed that’s a pretty clear signal that they’re trying to wash their hands of you without finishing the job; and I’d go the route of suggesting that you’ll hire somebody else to finish the job if they are unable or unwilling to.
Sounds like Octopus have tried quite hard and Im sure at a fair expense to improve the system.
Im not sure what those noises are though, they sound quite loud? or do you have a very sensitive microphone? Air rushing around the system is usually more of a continuous swooshing noise that can go in waves, at least from my own experience. It took me a while to get rid of the air that would sit in my hot water cylinder coil.
It can unfortunately be quite hard on some systems to get rid of all the air, even the best engineers can struggle to get rid of it in some cases - some systems seem to be harder to clear than others. The sontex is less effected but as Marko points out it doesn’t tell you if the reading as a result is in error.
It sounds like there may have been some air trapped somewhere else in the system, in a radiator somewhere? that then worked it’s way over to the hot water cylinder when it switched between space heating and hot water?
Can you try bleeding the radiators again? What is the system pressure now?