No this is not normal at all, most systems are not clunking like this. I thought (I don't know every brand Inc Grant) when the ASHP switches over the flow is reduced or stopped to allow the diversion. This sounds to me like hydraulic back pressure or something snapping over once the valve gets to almost closed on the DHW circuit and that the pump is still running full speed or it is moving something loose as the flow hits the line? hard to tell just from a sound video.

This could also indicate the the system is using the DHW loop as a bypass and something is blocking part of the heating loop so in effect slamming the ball of the 3 port against the closing section on DHW.

Little test you can try:

Turn off the ASHP DHW and only start the system in heating, then try the opposite and only start the system in DHW and see if any of the sounds are there on either, if they are not it is likely something wrong with the change over function of the 3 port, back pressure, pump command or that element of control.

@ashp-bobba thanks for confirming this, I do notice that the water pump doesn’t modulate at all and pretty much runs constantly. We are still waiting for Smart Energy Homes to come and rectify this and the leaks, they have said someone should be with us next week hopefully!

@grantmethestrength Oh sorry to hear that, there should not really be leaks and clunking valves from a new installation, I assume its new as you have leaks? 

Good luck and please let me know what they find, it will be good to get an understanding of what it was, I have only ever seen something simular once before and that was hydraulic hammering on the 3 port as a result of a closed line much further down the circuit (kind of like TRV hammering on a large pumped system) 

So the Lone Ranger returned today! Even though we thoroughly described the fault and them agreeing it was probably the diverter valve, geuss what they did not come prepared with? OK maybe I am being a little unfair as they need to order the part but still. When we heard the clunk he said “yeah thats the coils in the tank!” So I asked is it normal and he said it is an issue with the Honeywell diverter.

Interestingly he said that it is well known that the Honeywell diverters that come with the Grant Aerona kits are prone to failure hence Grant has changed the ones they use now, my response to this was why then did they install it in the first place!

So once he climbed on his trusty steed Silver and rode off into the sunset he shouted something very non comital about coming back next week with the new diverter valve.

Oh and despite lots of grunting and straining, the compression joints on the mag filter and flowmeter are still leaking! 

Ending on a positive note he did dig a channel to help the condensate drain away from the unit. And he will concrete over it when he comes back.

However he seems to be ignoring the fact that the condensate is coming out of the side of the tray not the drain hole!

Hi-Ho Silver indeed!