Well I'm guessing that the temp sensor is positioned where it has access to the surrounding air, but isn't within the air-stream which gets drawn through the unit.

You'll need to place your sensor in a similar position.

• out of the rain/frost
• not directly touching a piece of metal casing

Perhaps the problem is that the Daikin sensor has 'come adrift' from its mountings, and is no longer able to accurately reflect the true air temperature.

@transparent Would it just have the 1 sensor that gives me my digital reading on main screen because that said something like2degrees at 5am.

I don't expect they'll use more than 1 temp sensor on the outside unit.

Look at your graph.
There are three areas of interest

The red sector is clearly below zero, which was probably the setting on your controller.

The BUH continues to operate in the amber sector...
... until the sensor reports that the ambient air temp is 5°C

@transparent actually missed that graph was freezing, was only looking around 4am. hopefully so by changing setting to minus 4 it wont kick in. Thought it would only kick in if i was calling for heat and heat pump couldn't mange without the back up. Didnt envisage it ever kicking in tbh and def not when heat wasnt needed.

Like any other domestic 'frost-stat', the BUH temperature system is there to protect your pipes from freezing.

It has no concept of whether 'heat is required or not'.

The key temperature is +4°C  That's when the volume of the water is greatest.
If the water in your pipes has frozen and then melts, the point at which a 'burst' occurs is +4°C not 0°C

It's only safe to lower the set-point to -4°C  if there's anti-freeze (ethylene glycol) in the mix.

@transparent oh yeah i get you now, the flow wasnt for loops just o keep stuff from freezing, do ye mean antifreeze in ufh water thats going to loops or antifreeze in some part of the unit, plumber or daikin installer, who would put it in just s i know who to ring?

Posted by: @newhouse87

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@transparent oh yeah i get you now, the flow wasnt for loops just o keep stuff from freezing, do ye mean antifreeze in ufh water thats going to loops or antifreeze in some part of the unit, plumber or daikin installer, who would put it in just s i know who to ring?

To test if this is the cause of energy consumption, set the temperature down so that the heat pump stops, as you do with the overnight setback, then increase the Equilibrium Temperature setting above the present outside air temperature. There could be another sensor actually attached to the pipework, rather than the air temperature sensor, which is initiating the frost protection, so there may be a delay before it operates, since the pipework may have to cool down.

 

@newhouse87

I forgot to mention. Have a look at the manual for the controller, there may be an icon on the controller display which indicates if the BUH is operating.

Posted by: @derek-m

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Posted by: @newhouse87

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@transparent oh yeah i get you now, the flow wasnt for loops just o keep stuff from freezing, do ye mean antifreeze in ufh water thats going to loops or antifreeze in some part of the unit, plumber or daikin installer, who would put it in just s i know who to ring?

To test if this is the cause of energy consumption, set the temperature down so that the heat pump stops, as you do with the overnight setback, then increase the Equilibrium Temperature setting above the present outside air temperature. There could be another sensor actually attached to the pipework, rather than the air temperature sensor, which is initiating the frost protection, so there may be a delay before it operates, since the pipework may have to cool down.

 

so do you mean set equilibrium temperature to like 10deg overnight? Would that not mean its v likely to come on then? I can look at actuators in sensors settings when heat pump is running, i looked this morning and pump and compressor were def on and i think buh said on aswell, if it happens again i will know to look out for it. NO icon on manual for buh active.

 

@newhouse87

No, I didn't mean set the ET to 10C overnight, I meant to try the test now before you go to bed. Initiate a setback so that the heat pump is stopped, then increase the ET setting to see if the problem reappears. By doing so you will know if this is the cause of the problem.

@derek-m just changed it 5 minutes ago, no start of the pump yet anyway. Is it antifreeze in ufh water or actual unit you were talking about?

Posted by: @newhouse87

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@derek-m just changed it 5 minutes ago, no start of the pump yet anyway. Is it antifreeze in ufh water or actual unit you were talking about?

Unless you have a heat exchanger in your system, it is the same water that flows around the heating system, through the heat pump and through the UFH pipework.