This is often a problem when units are installed under a grant scheme. Some have two or three pumps running all the time! They should always be controlled by the heat pump controller and never wired separately or controlled by a central heating stat.

@dgclimatecontrol just to clarify, the water pump is inside the heat pump.  It is controlled by the Grant Smart Controller that also contains a thermostat.  There are no other room thermostats.

@grahamf To save wear and tear on the pump why could you not run weather comparison during the winter months only, and fixed temp. for the other months?

@iaack I could still use weather compensation to control the flow temperature, even with Pump Blockade = Yes, but the room thermostat in the Grant Aerona Smart Controller would turn off the heat pump compressor above 20C.  

In the summer, that is probably a good way to use the system.  Alternatively, I could just turn the space heating off completely.

However, I would like the system to be fully automatic.  I am also wondering whether heat Pump blockade = Yes might be good at other times of the year.  My inclination at the moment is to leave it set to No.

Posted by: @grahamf

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just to clarify, the water pump is inside the heat pump.  It is controlled by the Grant Smart Controller that also contains a thermostat.  There are no other room thermostats.

Im not 100% convinced that the pump blocade parameter controls the internal water pump.  It looks to me more like its intended to control an external water pump.  I could be wrong however.

Some heat pumps can operate their internal water pump in 3 modes

• on constantly,
• sniff  - on when compressor on, when compressor off on for eg 3 mins every 10,
• on only when compressor on. 

Based on a quick skim I couldnt find a config variable for that in the manual you have linked to so Im unclear whether Grant has already decided for you. 

I will try to work out what my Vaillant does.  When its cycled off consumption is ~8W.  That suggests the water pump is off, but maybe it turns it down to really slow so it can still monitor the flow temp (or maybe the claimed power consumption doesnt include the water pump).  If I find out I will post here.  Whats the claimed power consumption on the grant when its cycled off?

@grahamf Okay, I assumed you'd had an answer from Grants, I've not come across a Grant HP with its own pump not stopping. Their tech support is good so best ask them and how to get it sorted. could be costing you 1.5kW a day

@jamespa I tried both settings.  Pump blockade definitely controls the whether its internal water pump stops when the compressor stops.  

The energy reporting says zero, when the compressor is stopped, which obviously isn’t true.  I think Grant are working on various things in the data monitoring area.

Posted by: @grahamf

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@jamespa I tried both settings.  Pump blockade definitely controls the whether its internal water pump stops when the compressor stops

Interesting.  So if you set blocade it can't know the current water temperature in the system is, this must decide to switch back on on some other basis.  Reverse engineering control systems is fascinating, although I need to be careful not to spend too much time on it.

My Vaillant, which is currently cycling, has just cycled 'off' and the water pump has indeed switched off.  I have no way of knowing if it switches on from time to time, but I suspect not as it uses 'energy integral' (= integral (flow Temp-target flow temp) dt; where t = time) to decide when to switch on, so doesn't really need to know anything other than time and the current IAT, to which it can assume the FT is essentially equal.

The Grant engineer has given you the correct information.

If you let the water stop completely each time the compressor stops, consider what happens to the water in the pipes outside versus the pipes internally.

Keep the pump running. 👍 

My Stiebel GSHP does this too, but has a clever feature where it samples the water during shoulder seasons instead of continuously running.

My Grant Aerona3 circulation pump is set by default to run constantly this alone has cost £150 so far this year, if it is heating season I get the unit will be working but most of the summer I find it hard to understand why it needs to be pumping. (#Yorkshirenomics!!!)

Posted by: @grantmethestrength

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My Grant Aerona3 circulation pump is set by default to run constantly this alone has cost £150 so far this year, if it is heating season I get the unit will be working but most of the summer I find it hard to understand why it needs to be pumping. (#Yorkshirenomics!!!)

If you have rooms that get a lot of sun and which get far warmer than the others, you could maybe try to convince yourself that having the pump circulating even outside of heating season allows for at least a small additional movement of that warmth around the rest of the house.

I wouldn't advise trying to work out how big that effect is, though, as I suspect in most cases it's 'not large' 😐