Hi @snuffy , I have an Ecodan - slightly larger than yours- 8.5kw. You have one of the most readily adaptable sized heat pumps for retrofit applications which can be plumbed in with only 22mm primary pipes. It has a design flow rate range of only 9 -17 litres per minute (LPM) which, if operating at that kind of flow rate should be very quiet. Bigger heat pumps have to operate at much faster speeds.

So it might be worth asking your installer what is your current flow rate on your primary circuit? And.. What is the targeted temperature difference between flow pipe and return pipe? This should be averaging 5c

Another few questions might be - how do I control my pump speed? Do I really need a low loss header since a 6kw heat pump might only have a short run of radiators? Could it be reconfigured to operate off just one pump at a quiet 10 or 12 LPM depending on the DT target?

That would save you £200 for the low loss header and £200 for the second pump and around £100 per year in electricity driving the second pump. 

There may be a valid reason for high pump speed such as too much resistance through the pipework. But that would point to issues with pipe sizes etc. 

If you can talk to your installer now you may get a better understanding on how your system works and you may get a better set system commissioned properly.

PS. If you’ve got a Honeywell thermostat you can still operate your system using weather compensation. 
Hope this helps and gives you confidence to ask some important questions.

pps you can switch off the system briefly to allow air bubbles to clear before switching it on again. Some pumps have methods of bleeding trapped air. 

@snuffy don't give up , it sounds like your installer is "reasonable" - its a good thing that some radiators were mentioned as being in need of replacement, it suggests that heat emitter sizing and design flow temp has been thought about at least to some degree . I used to have  those fin things in my house as well, they are not the best (think mine dated back to house build time, 1970's - they are gone now though).

A spirovent is about 120 quid + his time to fit (easy job for a pro) and is guaranteed to remove air as a source of noise.

also its worth getting themto look at the design and control of the flow rate - are the pump(s) setup to modulate down when there is minimal load? they should. in which case at that point the flow noise will drop to next to nothing.

oh and mine's a retro fit from a gas boiler with 100% radiators. It can work. bigger house bigger unit but still a lot of the old pipework. Mostly new rads though.  It can work. but I do have 1 group of rads on a supply pipe that is slightly too small to be ideal - those are where I do get flow noise. So you may find there are just 1 or two places where pipework needs an upgrade.

But look at the air noise (really easy to solve) and flow rate (pump speeds) first.

Posted by: @snuffy

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I'm thinking if any are causing a problem, it's the one we have in the bedroom.

You shouldn't be left to ponder this.
Before a heat pump gets installed there should be an energy survey conducted (often by the installer).
That's how they know the size of the ASHP and heat-emitting surfaces for each room.
There shouldn't be any unknowns regarding whether a particular radiator is capable to delivering sufficient heat.

Such energy surveys are conducted to the PAS2035 standard.

Posted by: @sunandair

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If you can talk to your installer now you may get a better understanding on how your system works and you may get a better set system commissioned properly.

Quite!
It is a requirement of the Building Regulations, Part-L that you are provided with this information.

@snuffy I thought that for comparison, you might care to see a few shots of the lagging from the ASHP to the entry point into the house. I’m also putting a shot of the pipework fixings in the airing cupboard. The grey flexi pipes top centre were existing feeds to the shower unit. If you see some black lagging at the bottom edge of this photo, they are the lagged pipes from the Sunamp Thermino that is out of shot. Photos don’t seem to transfer, I’ll have another try with reduced filesize. Regards, Toodles

Still having probs with images, so just I’ll try just

two at a time! Regards, Toodles.

More photos of the lagged pipework. Regards, Toodles

And finally, the airing cupboard, overall, the system is very quiet and the only sound heard from any internal components is a faint pump noise if listening carefully with the airing cupboard open. Naturally, there is fan noise from the ASHP in the back garden but, this is drowned out by the ambient noise level from

nearby roads. I need to stand within a metre of the Daikin to hear it running above the ambient sound level. Regards, Toodles

I wouldn't be happy with the level of insulation or the fitting on the photos from @toodles

1. The brass isolation valves behind the ASHP remain entirely uninsulated
2. The insulation is compressed at a number of points by the use of nylon cable ties. (I can't tell if these are actually supporting the pipes, or holding an electrical wire to them).
3. That external pipe run is at least 5m, possibly 6m. I would expect to see 25mm wall thickness on insulation across that distance.

The internal bare copper pipes clearly don't comply with Building Regulations, Part-L 4.24

@transparent Thank you, I’ll take up the matter of insulating the brass valves with the installer, the ties are holding an electrical ‘trunking’ that carries everything non water based - and yes compression at these points does nothing to improve the overall insulation:-( The insulation is 70 mm diameter. The copper pipe is approx. 28 mm dia. Regards, Toodles

Sorry, I didn’t see the final comment about the compliance with buildings regs and insulation of pipes.The DHW system is a totally separate system and the pipework is insulated as required; the pipework you see is all there is to supply / lose background heat for the airing cupboard itself. The Sunamp Thermino DHW system has a specified heat loss of no more than 0.75 kW over 24 hours. We used to have a conventional insulated DHW tank and the overall heat loss was higher than the total we experience with the new system. There is only a small area of external wall to the side of the airing cupboard which is cavity insulated - the cupboard backs onto the bathroom and the ceiling in the cupboard has the usual plasterboard and above this is 600mm of loft insulation plus some boarding sandwiched between older and additional insulation. The heat loss from this pipework does supply some residual warmth in the cupboard - but as I say, far less than the previous gas CH and DHW arrangement. Regards, Toodles.

Building Regs Part-L 4.24 covers pipework insulation for both DHW and space heating.

There are some comprehensive online guides to insulation which are worthwhile reading.
It's unfortunate that most of them are USA-based and the charts are in inches.

Note that heat looses are specified in watts per metre: W/m
The longer the pipe run, the greater the loss.

Since the difference between Flow and Return is around 5°C
you really don't want to lose even 1°C before the water has even entered the house!

Regarding the external pipe-run, I did attempt to have as short a run as possible to reduce losses; I wanted to install the ASHP much closer to the airing cupboard area but no installer I tried felt it wise to install at height on the back wall. There would have been issues with access for servicing as well as possible vibration and noise transference. Reluctantly, I accepted the position it is in now and the longer pipe-runs. Regards, Toodles.