I can only speak from our own experience and the optimal flow rate for the Global Energy Systems ASHP is over 30 litre and it doesn't trigger alarms. 40 litre seems high, but I'm not an expert. Will be interesting to see what others say. 

28mm pipe can carry 16.8kW of power if the difference in temperature between flow and return is 5C, which it probably is. This means that assuming the pipe is not kinked or set up like a rollercoaster, it is not the pipe limiting the flow to 30L/m by itself.

My best guess is that your unit is modulating its power downwards because your house doesn't need 14kW right now. I actually emailed Mitsubishi to ask what their minimum output is yesterday, so I can update with what they say if they get back to me.

Have you been cold the previous three winters? If not, I would just wait to see what happens and not worry about it. Assuming the flow rate was limited by something - be it a pipe or a connection or a pump or anything else - it's still able to provide almost 11kW. It's possible that the length of the pipe run is having a limiting factor, but I don't know how to work that out. Again, I'd wait and see what happens when it's actually cold.

Posted by: @benseb

A question for those of you in the know

We have an Ecodan 14kW. It was installed about 12m from the tank (due to aesthetics and an existing oil tank concrete base). 

The installer used preinsulated pipe which was buried.  But it was 28mm which I’m now picking up isn’t big enough. 

We have an 80L buffer. Two pumps, one on the flow and one on the return from the heat pump to the buffer, which seems to be standard for Mitsi according to their manuals.

40-70 pumps on full. 

Our flow rate is 29-30. It’s not affected by radiators etc as the buffer separates the internal circuits off. 

I’ve been told the flow should be closer to 40. So I guess the only way is to replace the preinsulated pipe?

Just gathering opinions really. We will probably see out this winter and see what COP we get (was installed 3 years ago but have just tuned the WC curve etc)

Installer says flow rate is fine!

Our 14kW Ecodan also uses 28mm pipe.  We have no buffer.  The minimum output of your Ecodan is on p 69 of the link below.  The 14kW Ecodan needs 40l/min at its nominal speed. 

Hopefully you won't need anything like 14kW most of the time so a lower flow won't matter.    

LIBRARY.MITSUBISHIELECTRIC.CO.UK "https://library.mitsubishielectric.co.uk/pdf/book/ATW_Databook_R32_2020#page-68-69"

Ecodan ATW Databook R32 2020 - Document Library - Mitsubishi Electric

That’s a good point about output. I’ve been checking when it’s just ticking over at 25-30c flow temp. 

I’ll check again when it gets cold. 

it was fine last year aside from one day when it was about -6c outside and I got a flow fault. But that’s below design temp anyway. We have an immersion in the buffer tank that we can use with excess solar so switched that on when it was ultra cold. 

let’s see what this winter brings!

Posted by: @benseb

A question for those of you in the know

We have an Ecodan 14kW. It was installed about 12m from the tank (due to aesthetics and an existing oil tank concrete base). 

The installer used preinsulated pipe which was buried.  But it was 28mm which I’m now picking up isn’t big enough. 

We have an 80L buffer. Two pumps, one on the flow and one on the return from the heat pump to the buffer, which seems to be standard for Mitsi according to their manuals.

40-70 pumps on full. 

Our flow rate is 29-30. It’s not affected by radiators etc as the buffer separates the internal circuits off. 

I’ve been told the flow should be closer to 40. So I guess the only way is to replace the preinsulated pipe?

Just gathering opinions really. We will probably see out this winter and see what COP we get (was installed 3 years ago but have just tuned the WC curve etc)

Installer says flow rate is fine!

Hi Benseb,

The fact that it has been operating correctly for three years should provide you with the answer.

Setting weather compensation should not have a detrimental effect on operation, and should improve overall efficiency. Remember the old adage 'if it's not broken, don't fix it'. 😎  

Posted by: @kev-m

Our 14kW Ecodan also uses 28mm pipe.  We have no buffer.  The minimum output of your Ecodan is on p 69 of the link below.  The 14kW Ecodan needs 40l/min at its nominal speed. 

Why be like that and not also say the minimum output of an Ecodan is generally 3-4kW in above-zero ambient temperatures.

Although are you sure this isn't about a monobloc unit on page A-58? That has a wider 2-7kW minimum range depending on ambient and flow temperatures. I think if you bump into the 6+kW minimum often, that can be problematic and may mean the heat pump is oversize.

@mjr 

Be like what?  I was trying to be helpful and show the questioner the whole picture rather than just quoting one number.  That link has lots of other information too.  I always like to see a link rather than just an opinion. 

And yes I quoted the wrong page so thank you for pointing that out; the monobloc 14kW Ecodan is on p 58.    

Posted by: @kev-m

I always like to see a link rather than just an opinion. 

I like to see both. I admit it irritates me a little when only a link is mentioned because before getting our heat pump, I read lots of forum posts where no answer was given, only a link, and that link has broken: maybe the linked site moved the file, or maybe the link was incorrect all along. So please, think of future people reading these discussions ☺