Ok. I'm just checking whether there was any manual intervention at 8am-ish on Friday.
As you say that there wasn't, then something has occurred to knock some sense into the heat-pump.

That energy went somewhere...
... either to DHW or room heating.

What size is the DHW tank?

@derek-m no didnt go below zero, last friday on chart approx2-3 deg at 4am when i had such high usage. There is buh on unit but dont think that comes on much if at all. Has frost protection alright, have seen it before and lwt drops when it kicks in. Just dont get why its flowing when no call for heat. Read something online about blower relay switch malfunction.

@transparent Dont know where it went, none of my dhw cycles at night time anymore, tank is 240l i think.That usage is very excessive per hour, i have setback on programmable stat with last few weeks to not have usage at night time and then this happens which is worse usage.

Posted by: @newhouse87

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@derek-m no didnt go below zero, last friday on chart approx2-3 deg at 4am when i had such high usage. There is buh on unit but dont think that comes on much if at all. Has frost protection alright, have seen it before and lwt drops when it kicks in. Just dont get why its flowing when no call for heat. Read something online about blower relay switch malfunction.

Is the BUH rated at 6kW and is it enabled?

Do you have any record of the DHW tank temperature during these night-time antics?

240-litres looks like a great place to dump a shed-load of energy.

Posted by: @newhouse87

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dont get why its flowing when no call for heat.

I would be looking at the flip side of that coin.

Something called for heat. But it shouldn't have done.

There are three main contenders in my mind:

• valve opened/stuck/broke
• temperature sensor faulty, or possibly its connector(s)
• software malfunction

@derek-m not sure what its rated at, says in manual very limited use if at all.

@transparent no i jst know the current temp of it now at 42degrees and scheduled at2pm to heat to 48, Had 2 showers yesterday before scheduled period and haven't had post gym shower this morning yet so current temp seems ok for normal operation and no extra energy. Its why the heat pump is producing energy at all when no call for heat is the puzzling thing. Its off now as it should be so not sure if valve stuck.

Posted by: @newhouse87

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@derek-m not sure what its rated at, says in manual very limited use if at all.

The rating should be specified somewhere in the manual. What does the manual state about when the BUH should operate?

@derek-m says capacity of backup heater @: t design -10deg 9kw

Posted by: @newhouse87

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@derek-m says capacity of backup heater @: t design -10deg 9kw

Look through the controller settings and see if the BUH is enabled and the value of any temperature setting.

It doesn't matter what the manual states about the BUH operating only rarely.
That's just declaring what it's meant to do.
But we're looking at a fault occurring.

Where are you reading the DHW tank temperature?

Is this on the heat-pump controller, or a (digital) thermometer on the tank?

My tank (thermal store) will always output 42°C
but that's just coz it's configured to do so.

The actual temperature of the water at the top of the tank would be higher than this.

It all depends where you're measuring and how.

I deliberately have an independent digital thermometer with two sensors on my tank (top-most in photo below).

It provides no feedback to the controllers or heat sources, but allows me to check if the temperature controls are operating as they should.

@derek-m it is enabled, dont think it says anything about temp. equilibrium temp 0deg it says in settings.