@athlonoc You don't need 24L/min for an 8.5kw heat pump, Mitsubishi's own manual states 15.2L/min, 24L is the absolute maximum so i'm not surprised its making a noise.

I sounds like you know how to change the speed on the controller, there are settings for 1-5 and check the flow rate, enter code 540 in the running information menu.

I would reduce this till you get close to 15L/min, I run at pump speed 2 and that gives 14L/min and that works fine.

If any of the main circuit is smaller than 28mm F/R you will get a fair bit of noise above 15 l/m, once the circuit has dropped off to a couple of emitters you would be ok on 22mm there after, many installations now have a split ring, this is where they find the old 22mm circuit, cut it and attach with 28mm tee to allow the flow to run in both directions, this making the flow even in both directions, for example if evenly split, 24 l/pm split is 12 l/pm in each direction both from and to 28mm main F/R which is fine at the flow.

Please see attached, hope this helps.

@gary 

Thank you

Just a couple of points to note. When I reduced the flow rate I did it by reducing the speed on the pump in the loft and didn't change the settings on the FTC6. That pump being the Wilo pump as in the above pictures. Would I be right in thinking the pump speed control on the FTC6 controller would increase the speed of the Wilo pump?

Also the issue I then found with reducing flow rate eventually I had L9 errors. I think I went as low as 9l/min but kept it steady at 17l/m. We almost believed we could handle the noise at that speed but the system just wasn't happy.

I'll have a little play around.

Just a further note. Is it common to have to put pressure in the system almost once a month? It's set to around 1bar but after a few weeks it drops considerably. I've checked all air valves, and checked for any leaks at both internal filter and the outside filter

@athlonoc you don't have a mitsubishi preplumbed cylinder so the FTC probably can't control the pump speed but that is easy to check on the FTC go to service, code is 0000, then down till you see pump speed, note what setting its on and then change it up or down.  You should be able to here the change in pump speed if its controlling it but I doubt it is.

If it doesn't change speed then you will need to manually change the speed on the pump as you did before.

You just need to work out what setting on the pump gives you around 15L/min on the FTC.

To check flow rate on the FTC then you go to same service menu, then go to running information and enter code 540, this then displays the flow rate through the system.

@athlonoc Its unlikely the FTC is controlling a 3rd party pump (Wilo) so thats just on the pump control, you will need to run this system at least 15l/pm. if your system looses pressure you will get additional turbulence within the water circuits. It is not normal to loose water even over a year. My house was filled to 1.5 Bar 2 years ago and is still at 1.5 Bar and had no top ups.

If you cannot find a leak anywhere then I can point you in the right direction for a couple of places.

1) Inside the condenser cover of the Ecodan is a pressure relief valve, if this lets by you would not notice it as this water would mix with the condense drain, we noted that all the Ecodan PRV's seem to not seat correctly after discharging and drip slowly over time. (its worth checking but note, you should not take the cover off unless you are competent at isolation as you will be exposing the electrical connections) 

 2) If you have rads, there could be the smallest leak during heat mode as the pressure rises slightly, the small amount of water evaporates as it touches the warm pipe never to be noticed. If you suspect this you can tape white clean tissue to each rad's connection throughout the home and remove in 1 month time, the connection thats leaking will discolour the tissue with a brown or rust looking deposit.

Hi Gary,

Thanks for this info. I had done this without realising to a degree as I had noticed that when I looked at the commissioning wizard during the pump speed changes on the FTC6 it remained at 24l/min. So I guess it conformed then that it wasn't having an impact.

Its been very easy to control the speed down to 15 or 17l/min as I've done that in the past using just the Wilo pump speed setting, but the inevitable happens and within a few weeks at most the system then crashed with a flow rate error ( L9 ). So we feel trapped with high flow rate.

@ashp-bobba 

Hi and thank you for this advice. I'll get that done today and see what comes from it. With it being a new system I guess the discharge water might not be brown / rusty. However I think the inhibiter that is used is blue and i remember when they drained the system for another issue they drained buckets of a water that had a bluish tint. Great idea and do that now.

Report back. Thanks