@kev-m

The thermometer is linked the Passiv system and you can see the temperature on the graph which is placed in the lounge.  There is no other thermostat in the system and all TRV's have been set to their max setting.

I've spoken to Passiv and they have heat curves configured in their system that control when the heat pump will be requested to turn on based on the target temp being requested.  They have said their system is not requesting the system to switch off when you see the cycling pattern illustrated in my last graph and that is something the Grant HP is doing.  It's difficult to know who to believe because Grant say their system is dumb and controlled externally.

I think the real problem though is the flow rate from what I can gather from all your great responses.

Posted by: @cathoderay

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Isn't the (max available) power (in kW or could for example if it was a car be HP) constant, but if the unit only runs for 75% of the time, then it uses/provides 75% less energy than it would if it ran 100% of the time (in car terms, if you only drive for 45 mins (still at top speed) out of every year, you use 25% less fuel and cover 25% less distance than if you drive for 60 mins of every hour).

Probably not, because the car doesn't travel as far while it is speeding up after being stopped. That's why we don't want heat pumps to be running too hot, stop-starting and letting the refrigerant cool between runs, whether due to cycling or boiler-style on-off thermostats.

@derek-m 

You just reminded me I have a pizza oven thermometer which I can use

In my lounge 

There are 4 radiators.  I took the readings from 

2m K2 radiator new - top : 32c,  bottom : 24.8c

1m K2 radiator new - top : 34.1c, bottom : 29.8c

1.6m K2 radiator new - top : 22.3c, bottom : 17.1c

low height 43cm double radiator existing - top: 35.7, bottom : 32.9

@soniks clear evidence your rads aren't at all balanced. Give it a go with a pair of pliers. You'll be amazed at the difference it will make to your house once they are all balanced.

I've been around today rebalancing ours actually. My tools are a Letherman and my hand. Seems to do the job

Posted by: @allyfish

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But I would not be without a log burner as a secondary heat source. The log burner provides comfort boost downstairs mid-afternoon to evening and gets the lounge to a more cosy 21-22degC,

And of course it doesn't need electricity to run, very useful in power cuts. I do have an inglenook, but it has an open fire on fire dogs with a large cast iron fire back. It doesn't get lit regularly, but is there for special occasions and of course emergencies. I have wondered about a wood burner, but call me very old fashioned, I do like the look of an open fire, even if, as has been said, they are a recipe for red faces and cold ankles, and most of the heat from the fire goes up the chimney.

Posted by: @mjr

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Probably not, because the car doesn't travel as far while it is speeding up after being stopped. That's why we don't want heat pumps to be running too hot, stop-starting and letting the refrigerant cool between runs, whether due to cycling or boiler-style on-off thermostats.

Very good point which I don't disagree with at all. I was really just using the car engine power/fuel consumed analogy to help clarify in my mind the difference between kW and kWh. Maybe I (I nearly did) should have used a single 2kW (power) Argos convector heater in a room with a 2kW (energy) heat loss as an analogy: over an hour, if it is on all the time, it will keep the room warm, but if it is only on 50% of the time, it will run at 2kW (of power) when it is on, but it will only use/deliver 1kWh (of energy, 2kW x 0.5h), and the room will be cold.          

Posted by: @soniks

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@derek-m 

You just reminded me I have a pizza oven thermometer which I can use

In my lounge 

There are 4 radiators.  I took the readings from 

2m K2 radiator new - top : 32c,  bottom : 24.8c

1m K2 radiator new - top : 34.1c, bottom : 29.8c

1.6m K2 radiator new - top : 22.3c, bottom : 17.1c

low height 43cm double radiator existing - top: 35.7, bottom : 32.9

 

I would suggest that you start by checking that both valves on your 1.6m K2 are fully open. If they are then try to trace back along the pipework for any valves or any form of restriction.

@batalto 

Will give it a go for sure but I do remember when the plumber fitted the an additional circulatory pump he rebalanced all 23 radiators and towel rails and still couldn't get all the radiators to warm properly.  

@soniks from my experience balancing rads takes quite a bit of time (99% waiting around). I'm wondering if he could be bothered with tweaking and waiting.

@derek-m 

I checked the lockshield on all of the lounge radiators and they are all fully open.  Unfortunately the piping is all under wooden flooring which is going to be a pain to take out and understand piping setup.  Hence thinking of putting UFH and insulation underneath

@soniks have you details of the second circulation pump fitted? Maybe a photo or something? Have you a flow setter / gauge on the system or any way of checking and setting the flow? It's quite a fundamental item for ASHP. The Grant Aerona range don't measure flow, and the internal pumps are fixed speed, but can be pre-set to one of 3 speeds. Most simpler central heating pumps these days are the same. Based on the very high flow and return temperature you have of 12degC, I'm pretty sure a fundamental issue is lack of flow, for reasons not clear. Let's check out what pump is fitted, and see if it's man enough for the job. If it is, there's another issue to tease out. I have a 24 radiator single zone system with 28mm, 22mm and 15mm copper pipes, and no problem getting flow with the built in Grant pump and a secondary small Grundfos (UPS3) fixed speed circulating pump.

Until there is adequate flow to all radiators, balancing them up is not really going to provide much benefit. You are robbing Peter to pay Paul. If there isn't enough circulating water flow, you'll never balance them properly.

The main pump in the Grant unit should be up to the job on it's own, but you also have a booster pump. OK, let's assume the secondary pump is up to the job. So why the high deltaT temperature drop over the system and the low flow? One other likely reason is a blockage.

The Grant unit does not have an inlet strainer to the plate heat exchanger which warms the water in the circuit. For that reason there should be a magnetic filter and strainer on the return to the ASHP, Grant's version that comes with the ASHP is 'Grant Vortex Max One' but Adey Magnaclean and other similar items do the job. They are low pressure drop items, great for removing ferrous contamination, but they don't stop small particles of contamination from blocking your ASHP plate heat exchanger however, which is why system flushing before commissioning is so important. This is especially so when ASHPs are retrofitted to older heating circuits where the pipework and system cleanliness can be poor. You explained your system had a faltering install in stages, do you know if it was properly flushed out & cleaned before being commissioned?

Plate heat exchangers can be reverse flushed and unblocked, it's not a disaster. Has anyone checked this for you? (installation manual page 66 item 29)

@soniks

Now try closing the TRV's on the warmer radiators for a period of time to see if more water is pushed through the colder radiators. Try bleeding the radiators and see if there are any airlocks.

@allyfish it's the first time got the measurements from the heat pump but in my metering dashboards I can see its thereabouts