@jamespa 

Yes the EHSC has a pump with these charasteristics according to the Manual

Ok well in that case I defer to the more detailed comment by @johnmo above.

There are ways to fix the pump capacity (if it's actually a problem). 

If the buffer tank is unbalanced then it is reducing efficiency, roughly 3% per degree C measured between flow in from the heat pump, and flow out to the radiators, that's just a fact.

I would measure the difference above (mid season) and then decide whether the cost matters to you.  If it does then insist on a change.

@johnmo 

That is a different concept to that I was trying to get across in my broken Portugese sprinkled with English. I was hoping to ditch the secondary pump because:

1 It is a PWM pump without the variable speed facility. The local Grundfoss agent says it should not have been used, but I think because it is old rather than necessarily it's performance curves

2 It is using power, so presumably wasteful

Just to confirm - I have no house thermostat and work entirely on weather compensation

I cannot check until we get to colder temperatures, but I seem to recall that the secondary pump is not controlled by the Hydrobox, i.e. runs all the time.

I will check its electrical connection tomorrow

Posted by: @davidalgarve

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@johnmo 

That is a different concept to that I was trying to get across in my broken Portugese sprinkled with English. I was hoping to ditch the secondary pump because:

1 It is a PWM pump without the variable speed facility. The local Grundfoss agent says it should not have been used, but I think because it is old rather than necessarily it's performance curves

2 It is using power, so presumably wasteful

Just to confirm - I have no house thermostat and work entirely on weather compensation

In addition to any response from @johnmo please read my post above which gives you some way to determine how much it matters .  If the power consumption of the second pump is a concern so the arithmetic to see if it's significant.  Central heating pumps are usually 50W or less.

@jamespa I was almost using your piece above as my script to explain what I wanted to do. I had even done a translation into Portuguese, but I had no answer to the possible inadequacy of the inbuilt Mitsubishi pump

Posted by: @davidalgarve

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@jamespa I was almost using your piece above as my script to explain what I wanted to do. I had even done a translation into Portuguese, but I had no answer to the possible inadequacy of the inbuilt Mitsubishi pump

Unfortunately the plumber may be right, or he may not.  Without doing the calculations (or the experiment) it's impossible to tell.  

However more or less any plumber should be able to do these calculations and show you the answer.  If the Mitsubishi pump isn't adequate then it needs to be supplemented or replaced.

Comparing your heat pump, circulation pump and the secondary pump curves they are very similar. So assuming the heat pump isn't 10s of metres away there should be no issues deleting the secondary pump and buffer.

@johnmo I have checked the connection of the secondary pump and it is on "Out 2" which is designated for "Pump 2 - Zone 1". Strangely "Out 1" designated for "Heating and DHW" has no connections.

I am a little uncertain how you are comparing  the EHSC pump, (for which I previously provided the curves), with the secondary, Grundfos UPM@ 25-70 180. 

I am attaching the curves I have found for the latter and if I do one comparison on the max speed curve at 40kPa on the EHSC and 4.07mH on the Grundfos (which I believe are the same), the EHSC pump delivers 22l/min and the Grundfos delivers 38l/min.

However, my 87 year old brain doesn't cope well with more modern units so perhaps I am entirely wrong.

I dont know what speed the secondary pump runs at because the PWM control is missing, but it is not so noisy so I suspect not at maximum. If I were to go ahead and accept the lower flow rate from the EHSC pump, would that be a disaster?

Posted by: @davidalgarve

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EHSC pump delivers 22l/min

No that is 2.2 m³/h, so 2200L/60 mins, is 36.66L/min. So the head flow curve is just about identical on speed 5 and max flow on the secondary pump.

If you need to operate at 4 bar head loss you have major issues.

Posted by: @davidalgarve

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dont know what speed the secondary pump runs at because the PWM control is missing,

Should be full speed i.e. top running curve.

Posted by: @davidalgarve

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Strangely "Out 1" designated for "Heating and DHW" has no connections.

You have a diverter valve upstream of the buffer which takes care of the DHW heating flow.

@johnmo Thanks for the correction and it sounds promising. I have no idea what head loss I am working at and don't know what the flow rate is, so would it be useful to measure the current drawn by the pump? I don't have a current vs head graph for the EHSC pump, but could, perhaps, use the Grundfos graph as an indicator.

Posted by: @davidalgarve

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don't have a current vs head graph for the EHSC pump, but could, perhaps, use the Grundfos graph as an indicator.

Think looking at the two curves, you will be near enough using the Grundfos one.