@jamespa Regretting I attempted this now. A very small amount of dirt in the filter, but L9 error now and won't start.

Posted by: @davidalgarve

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@jamespa Regretting I attempted this now. A very small amount of dirt in the filter, but L9 error now and won't start.

L9 = Low Flow error

Posted by: @davidalgarve

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@jamespa Regretting I attempted this now. A very small amount of dirt in the filter, but L9 error now and won't start.

Oh dear, sorry to hear that, isn't l9 low flow?

@f1p Yes understand that but why. Investigating air in system

Back working again now and problem was air in system. Flow rate is 17 l/min

Answer to question re flow rate put to Mitsu UK (Portugal is useless):

For a 12 kw unit the target flow rate is 32 lpm with a minimum of 14. Which would put this in the operating range that we set out.

 The installer will usually lower the flow rate form the target until the system is balanced and pushing heat into the property.

Now where, in the menu, would they have that ability so that I can check?

Tried "Heat Pump Settings" and that is on 5 min 100 max so that is not limiting it.

It has gone up to 18 l/Min so perhaps the system is slowly winding it up (hope!)

With the input from @f1p and @jamespa I am persuaded that my problems are all related to low available flow rate, particularly as I have a record of a higher figure. However, I am uncertain why this is the case, e.g. is the pump being regulated down or are there other factors?

I had come to the conclusion that my problems started when I added DHW, which necessitated the addition of a three way valve and some additional pipe fittings that would have increased pipe friction. At that time I still had a second pump in the circulation to the radiators, so the available flow would be that from the two pumps in series and the flow would still have been sufficient for the radiator supply.

Before the onset of winter, the buffer tank was converted to volumiser and the second pump was removed. I had checked that the characteristics of the primary pump were similar to the secondary pump, but I ignored the extra capacity from two pumps in series. I also failed to take into account the extra pipe friction, particularly in the line to the radiators. 

This led me to think that the reduction in flow rate was due to increased  pipe friction and I hoped to confirm this by checking the flow rate to the DHW tank,  which is much shorter and almost certainly has less resistance.

I was very surprised to find that the flow rate to the DHW tank was almost the same as that to the radiators, i.e. Setting 3 > 11 l/min and Setting 5>15 l/min

So is the pump defective or is the flow rate being regulated down?

It would be useful to compare flow (l/min)/ power (kW), against the published performance of this Grundfos pump and I wonder if this data is collected by the MelPump app?

Posted by: @davidalgarve

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So is the pump defective or is the flow rate being regulated down?

 

You can possibly check the latter if it has a PWM connector which is separate from the pump power supply.  Just pull the PWM cable and most PWM pumps default to max speed.

When you had a buffer you didn't exactly have two pumps in series (thats the point of the buffer), but there was more pump power.  Its possible that could have made a difference.  Opinions seem to differ on whether two pumps literally in series (which is what you would have if you reinstated the second pump but not the buffer) is acceptable ; personally, so long as they aren't widely mismatched, I cant see why not and neither have I heard a rational explanation.  Assuming you still have the original pump then simply replacing it into the circuit may be an option.  

@jamespa Thanks for your comment James. Of course you are correct and I think I was suffering a little brain fog in suggesting that the pumps were both contributing to the flow. Astonishing rain and wind here and some flooding so have only just got around to making further checks.

I had to remove the circuit board to get to the pump and I find it is a Grundfos UPM3 15-75 130. As you suggested I pulled the PWM connector with no effect on the pump speed as shown on the 'Commissioning Wizard' i.e. 17l/min.

The Grundfos pump is showing a green LED which on some models of the UPM3 indicates "No external control", but I can't think that applies in my case where the flow changes when the pump speed is changed from e.g. Setting 3 to 5.

Consequently, I am still perplexed as to why the installed pump is not delivering anything like its rated flow.

To reinstall the second pump would require some plumbing and reliable contractors are hard to find. Additionally one reason I was keen to remove it, was that although it is a PWM pump, the PWM controller was not supplied, i.e. no speed control available.

I am not sure where I go from here.

Posted by: @davidalgarve

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I am not sure where I go from here.

I have been wondering that myself.

The fact is that, even with the buffer (meaning that the secondary pump doesn't have to push water through the pipes to the HP and the heat exchanger) your flow rate was hardly spectacular.   So before leaping to any conclusions I think a bit more thought is needed.  Is the heat pump well oversized, is the emitter system simply under specified in terms of its pipework (or correctly specified, but not for an oversized heat pump).  Those are the next questions to answer IMHO.

Can you (a) remind me what the previous flow rate was and was that primary or secondary

Describe your emitter system particularly with reference to things that will cause friction 

Have any measurements of house loss (eg from consumption/heat delivered as measured by the heat pump

Also can you remind us the model of heat pump

and the model(s) or better still performance curves (I think you said you have them) of the water pumps

Also re

Posted by: @davidalgarve

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of a three way valve and some additional pipe fittings that would have increased pipe friction

Can you be more specific and I presume its a diverter valve (ie either DHW or space heating but not both)

These may point in a direction.  There are probably 5 choices

• refit the buffer, accept and work around the limitations
• leave as is, accept and work around the limitations
• add an additional water pump
• replace the existing water pump with something beefier
• do something with the heating system to improve throughput

Currently there is insufficient information to determine which is the best option.