Welcome to the forum and I am sorry you are disappointed.

In fairness this time of year is by far  the most expensive and the most noisy time for heat pumps.  You daily consumption over the past few days is likely to be around three times the mid-season consumption, and this is also the time of year when heat pumps have to work very hard to defrost, which can be noisy.  Most of the season it wont be doing this.

However you shouldn't be hearing the the various pumps, volumizer etc. and the sound of rushing water in the pipes.  The latter suggests you may have air in the pipes which needs to be got out.  I would ask Octopus to come back and take a look.  It can take a while to get air out of any newly filled heating system BTW.  I had a radiator that needed to be bled once a day for a month to stop gurgling sounds, even though auto-bleed valves are fitted.  This is inevitable because the newly introduced water has dissolved air which comes out of solution over time, there is absolutely nothing an installer can do to avoid this.

If you post some more detail about 'doesnt heat the house very well' and a bit about your house we can help.  Many people make the mistake of running heat pumps like a boiler, with on/offs, setbacks, thermostats and TRVs.  You have to forget more or l;ess everything you thought you knew about running boilers (much of which was wrong even for boilers!).  Heat pumps work best when run constantly with the weather compensation curve turned down as low as possible and influence from thermostats minimised or eliminated altogether.  This is, in most cases, both the most comfortable and the cheapest (for once mother nature works in our favour).  It takes a bit of a leap of faith but, done right, it may be much more comfortable than your previous system was.  Give it a few weeks and post some more info and I'm sure we can help you improve the experience.  Do get Octopus in about the noise however!

Also have a read of this introduction to give you some background.

@razz stick with it.  There's loads of advice on here.  The weather compensation thing is the way forward re actual operation. I had a 37 year old oil boiler replaced.  I have tuned it with weather comp settings so it is running utilising the internal settings in the ASHP to ramp down rather than switching on and off with a room stat.  This way we have a house that is warm throughout all the time (before we were cold some of the time and the bedroom was always cold ) and cost wise is about the same as when we were running with oil. Hope this helps. We are much more comfortable.  

Thank you both for your kind comments. I've had an emergency engineer come by yesterday and dismiss it all.

I've asked for a more experienced one to come on monday. 

I really hope it's all teething problems, cos it's just unbearable right now. The heat pump is just a few feet away from our rear extension and my poor mum can't sit in that room any more.

Posted by: @razz

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I've had an emergency engineer come by yesterday and dismiss it all.

🤣 what exactly did he dismiss and why?

Well, the guy came out, turned the heat pump to max, we stood outside near it for a bit, and acted shocked that I thought the sound was loud, tbf, it didn't sound so bad (still quite loud).

We went inside and you could hear a low rumble, he was dismissive of it, saying the fridge in the room sounded louder, the fridge is loud, but it's not an annoying deep drone. You definitely can't hear the fridge in other rooms.

Then we looked in the cabinet with the tank and the (circulation pump?) and volumizer. He guessed that the noise in my room might be from circulation pump, so he turned the speed down on the motor (it hasn't helped).

We went into my room upstairs, and he could hear the low drone, but apparently it wasn't that bad. Then he left.

The sound is even worse in the actual bed, cos the mattress seems to act like a stethoscope for the droning sound of water/circulation pump and the heat pump. You can definitely hear when the heat pump comes on. Last night I had to flee to my front living room to get some sleep.

My mum watches TV sitting where the photo was taken from, and she can't any more cos of the rumbling of the HP. It's a low 180Hz (approx) sound, as per octopus recommended app Decibel X.
Some more pics, to give a context of what the system is like:

Also, when touching the various tanks and pipes, you can definitely feel the volumizer vibrating. 
And a recording of the sound:

Door closed

Door open