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What happens when the outside temperature exceeds the upper WC point?

bontwoody · 2025-04-03T14:01:13Z

Ive posted this following a comment in another topic which I didnt want to take off track. I have always thought that when using a weather compensation curve, once the outside temperature exceeds the top set point (eg a flow temperature of 40C at 17C outside), that the heat pump switches off its heating function. However it was suggested that what might happen is that the flow temperature just stays at 40C and does not change. I can see the logic of this as at the other end I would not expect the heating to switch off at say -3C :-) The problem with this is though that as the outside temperature rises, if the heat pump stays on then it will cause the house to overheat and cost money needlessly. This scenario would require the user to actively turn the heating off. Does anyone have a definitive answer to this, or do different heat pumps handle the situation differently?

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Judith

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05/04/2025 12:07 pm

@jamespa not found the hysteresis to be a problem yet. The house warms up a lot in the sunshine so it’s only back to our desired temperature by later in the evening, if at all (high thermal mass). We toggle between ‘active’ and expanded depending on the amount of sun.

I might turn the setting of outside temperature down further (present 17C) in summer to prevent any heating on a cool night. Happily fiddling right now!

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Mars

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07/04/2025 7:56 pm

The focus of this week’s podcast recording is on “Heat Pumps & What To Do in Warmer Weather” and I’ll pull questions from the the thread so far, but if anyone has other questions on this subject, please pop them below, DM or email me (editor@renewableheatinghub.co.uk)

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Mars

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23/04/2025 8:57 pm

@bontwoody asked your question at the start of this thread to the panel. An interesting reply from Graham Hendra.

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bontwoody

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Topic starter 23/04/2025 9:38 pm

@editor Thanks Mars. Interesting talk. I will just point out however I don’t actually run my heat pump at 40C when it’s 17C outside! Don’t know why I plucked that figure from the ether 😆

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Mars

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23/04/2025 9:51 pm

@bontwoody 😂 does your unit turn off when a specific OAT is hit?

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bontwoody

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Topic starter 24/04/2025 5:21 am

@editor not via the WC curve but as @old_scientist mentioned the setting is in the FSV menu so I was able to set that to 19C rather than it’s default of 35 C OAT