@transparent reading from main  screen on front of unit panel. Reads 48 just after heatup so thinkits accurate.

has enable buh step 2 - yes

Whatever we're looking for is an intermittent fault.
It occurs, and then goes away.

If you look at the display a few hours later, everything might appear normal.

But something told that same controller to use energy in the middle of the night.

And yes... I think @derek-m is correct to be asking about the BUH.

9kW is three times the power of a standard domestic immersion heater.
It doesn't take much to be going wrong for it to be using energy like it's running out of fashion.

@transparent yeah its just annoying at this stage, maybe just disable buh, if derek m recommends that.

Disabling a feature could just be masking a poor solder joint in a connection to a sensor!

Wouldn't it be better to narrow down the search first before trying to eliminate a possibility which remains unproven?

What about buying a couple of cheap temperature sensors from Amazon?
We might find a design which holds results in memory so you can look back over them.

Posted by: @newhouse87

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@transparent yeah its just annoying at this stage, maybe just disable buh, if derek m recommends that.

This is an extract from the manual.

7.6.4 To protect the water circuit against
freezing
Frost can damage the system. To prevent the hydraulic components
from freezing, the software is equipped with special frost protection
functions, that include the activation of pump, internal heaters, and/
or backup heater operation in case of low temperatures.
However, in case of a power failure, these functions cannot
guarantee protection. It is therefore recommended to add glycol to
the water circuit. The required concentration depends on the lowest
expected outdoor temperature, and on whether you want to protect
the system from bursting or from freezing. To prevent the system
from freezing, more glycol is required. Add glycol according to the
table below.

Looking at the previous graph, the outside temperature was below zero for a period before the high energy usage. Did the same happen this morning?

Here is more info from the manual.

Backup heater
Backup heater operation mode: defines when backup heater
operation is enabled or disabled. This setting is only overruled when
backup heating is required during defrost operation or malfunctioning
of the outdoor unit (when [A.6.C] is enabled).
# Code Description
[A.5.1.1] [4‑00] Backup heater operation:
▪ 0: Disabled
▪ 1 (default): Enabled
N/A [5-00] Is backup heater operation allowed
above equilibrium temperature during
space heating operation?
▪ 1: NOT allowed
▪ 0: Allowed
[A.5.1.4] [5‑01] Equilibrium temperature.
Outdoor temperature below which
operation of the backup heater is
allowed.
Range: –15°C~35°C (default: –4°C)
(step: 1°C)

Auto emergency
When the heat pump fails to operate, the backup heater and booster
heater can serve as an emergency heater and either automatically
or non-automatically take over the heat load.
▪ When auto emergency is set to Automatic and a heat pump failure
occurs:
▪ The backup heater will automatically take over the heat load.

If you have anti-freeze in your system then lower the Equilibrium Temperature to the default -4C value.

@derek-m cheers man. No wasnt freezing this morning at 4am, was approx 2 degrees on panel, i was half asleep looking at it though, this i dont think happened during winter but i cant be sure of that as pump was running during the night anyway, only seems to be happening now im using set back at night time. So just change equilibrium temp to -4? How do i know if i have anti freeze in system, i know i have gas alright.

Posted by: @newhouse87

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@derek-m cheers man. No wasnt freezing this morning at 4am, was approx 2 degrees on panel, i was half asleep looking at it though, this i dont think happened during winter but i cant be sure of that as pump was running during the night anyway, only seems to be happening now im using set back at night time. So just change equilibrium temp to -4? How do i know if i have anti freeze in system, i know i have gas alright.

I would hope there would be a label fitted somewhere stating the concentration of anti-freeze added, if that is the case. If not contact your installer and ask if it was added, and how much.

The actual outside temperature might not be below freezing...
... but the heat-pump controller thinks it is.
That's what triggers the BUH.

Why not just log it to see what's happening?

There are some cheap temperature loggers (< £30) being used by reptile keepers to monitor their vivariums.
Search online for temperature logger.

Some have their own display;
others you plug into a USB post on a PC to recover the data;
and others send the data to an App on your smartphone.

If you can find one with an optional plug-in probe, then get that.

You can push a probe beneath lagging on pipes and tanks.

@derek-m cant see label but shur it must have been added, had no problems during winter. Changed equilibrium temp of building to -4. Just looking at actuators in settings, not sure but think buh said on this morning along with pump compressor etc when i was looking through it. Not 100% on that though. Thanks again man, hopefully that sorts it.

@transparent yeah might do that, where would i put it on daikin unit?

It wasn't below freezing last night, some sensor must be off, where would best place to check be? I doubt buh is even mean to come on if it just goes below freezing.