Can you explain the freeze stat function please? What is it supposed to to do? It us certainly to be described/labelled differently on other makes but there might be the same function.

So

Posted by: @ecodan-efficiency

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On my ecodan the minimum temp I can set the freeze stat function to kick in is +3 degrees C. How does that compare with other manufacturers?

So far as I can tell absolutely no control available on my Vaillant, it kicks in at 4C

Posted by: @judith

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Can you explain the freeze stat function please? What is it supposed to to do? It us certainly to be described/labelled differently on other makes but there might be the same function.

It switches on the heating (typically periodically or at a minimal value) - even if its switched 'off' - obviously provided the mains is connected - when the outdoor temperature falls below a certain value.  This function is also present in many boilers.  The idea is a fallback protection for pipes and equipment.  makes sense IMHO.

@judith Hi, sorry, I should have been more informative. The "freeze stat" function will circulate the water traveling to and from the heat pump in the event of the outside temperature dropping below a set value - so that it does not freeze.

When I've had this function turned on I don't recall the pump itself operating, or indeed the radiators being warm at all, although there seems to be a suggestion that the ecodan system will keep the water at 20 degrees (based on the screen in the settings).

Posted by: @jamespa

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It switches on the heating (typically periodically or at a minimal value) - even if its switched 'off' - obviously provided the mains is connected - when the outdoor temperature falls below a certain value. 

I don't think I've ever seen this function/setting before on our control panel for our Global Energy Systems machine, but that's hardly surprising. 

Mmmm...on my Ecodan it seems to operate at temperatures below +3C and when the system is not calling for heat. So during the overnight set back, if it is +3 or below,  it switches on the primary circulation pump to move the fluid but it does not switch on the heating. As the system has glycol added, the engineer switched it off at the last service as redundant. 

If the overnight temperatures are seriously sub zero, as in recently, then the auto adapt seems to bring on the heating to maintain the house at 16C regardless of set back until the next heating period hoves into view.

Posted by: @abernyte

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Mmmm...on my Ecodan it seems to operate at temperatures below +3C and when the system is not calling for heat. So during the overnight set back, if it is +3 or below,  it switches on the primary circulation pump to move the fluid but it does not switch on the heating. As the system has glycol added, the engineer switched it off at the last service as redundant. 

If the overnight temperatures are seriously sub zero, as in recently, then the auto adapt seems to bring on the heating to maintain the house at 16C regardless of set back until the next heating period hoves into view.

That all sounds plausible.  Neither heat pump nor boiler manufacturers seem to be particularly precise about what these sort of functions do.  The objective is clear however - to prevent freezing (of the unit itself and possibly the house pipework) during times when the heat source is otherwise off, such as vacation.  Its the sort of thing that modern electronics makes easy to do, but of course at the same time obscures the precise algorithm used!

My boiler system had an actual frost stat (a physical piece of hardware), which was wired basically to override pretty much all other controls if triggered, to switch the boiler on.  It was attached to the pipework so measured water temperature.  This could and did result in the boiler coming on in the middle of a very cold night even if I had it set to off.  That seems to me to be a very reasonable behaviour.

Posted by: @abernyte

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If the overnight temperatures are seriously sub zero, as in recently, then the auto adapt seems to bring on the heating to maintain the house at 16C regardless of set back until the next heating period hoves into view.

This sounds kind off odd. I run my ASHP on a room temp schedule, with a setback during the night to ensure it's off until morning (13 degrees because the house loses heat so quickly), and I've never witnessed this behaviour. Where would this figure of 16 be coming from? Have you activated Frost Protection on the melcloud app perhaps? (not to be confused with frost stat function).

No..simply by observation. I can be found about in the early hours and I have noticed that the temperature seems to be kept around 16C if it is -4/5C OAT.  It could be Auto Adapt getting a head start on the morning warm up or some other magic dust that Mitsubishi have sprinkled as the Frost Protection setting is off. 

Just checked my ecodan setting and mine is turned if so can only presume the system has antifreeze added 

Posted by: @ecodan-efficiency

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Posted by: @abernyte

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If the overnight temperatures are seriously sub zero, as in recently, then the auto adapt seems to bring on the heating to maintain the house at 16C regardless of set back until the next heating period hoves into view.

This sounds kind off odd. I run my ASHP on a room temp schedule, with a setback during the night to ensure it's off until morning (13 degrees because the house loses heat so quickly), and I've never witnessed this behaviour. Where would this figure of 16 be coming from? Have you activated Frost Protection on the melcloud app perhaps? (not to be confused with frost stat function).

I wonder if this related to the Holiday setting in the controller menu which sets a room temperature below which the heating will come on with a modest flow temp when the normal heating pattern has been turned off after Holiday Mode is activated. This has caught me out before when I expected the heating to remain off when I was on holiday only to see it running - I have lowered this temperature from its default setting of 15° since then.

Perhaps this particular setting also acts as a default lower room temperature even when the heating is following its day-to-day schedules?

I spotted our value ages ago buried deep in a document/menu but now can’t re-find it!

It will be the same 4C as JamesPa’s value, assuming it’s the default. And I see no reason to change it.

That’s consistent with our old gas boiler inside the then unheated garage which kicked in at 7/8C (and did on cold nights). But the ashp has outside (no glycol but dump valves) pipes and it’s better that they don’t get to freezing and use the dump valves. As long as everything is working either the nighttime set back or holiday mode temperature will be much higher.