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Siting of the external sensor on a heatpump

Air Source Heat Pumps (ASHPs)

Last Post by Batpred 24 minutes ago

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Batpred

(@batpred)

Noble Member Member

Joined: 2 years ago

Posts: 1138

Topic starter 10/09/2026 8:41 pm [#3160]

So I have been very happy with the pump doing hot water. Did a bit of cooling but no heating, of course...

But as an obsessive engineer, the thing is quite thoroughly "instrumented", lots of monitoring around it and something is odd with the sensors. Discussion in the family gets to "but is it causing a problem now?"...

But having just read Mars great sh*tshow book, the house at number 58 is what comes tomind. This is where, despite all the best efforts and all the certifications and logos, the ASHP never worked as as reasonably expected. It took a few years with the MCS circus causing havoc to progress "the diagnosis". Our goal is to sort it before it causes more than an odd chart..

The chart below plots the external temperature sensor with the weather temperature (plus a temperature sensor that we move around the home). All being well, we would expect the two external temperature lines to move along roughly in sync. But they do not.

So the best hypothesis is that the neighbours boiler is doing a lot of hot water around 9am (and by the looks of it, not getting into condensing mode). When winter comes, the boiler will do heating when it feels like and play havoc with our sensor a few meters away (and that is expected to drive the weather compensation..).

I checked the Arotherm Appliance Interface instructions and it clearly does not say much about locating the external temperature sensor, apart from the odd manual that goes as far as saying it should be below 2.5m high... So this seems a case of "all good and according to all instructions"..

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kW export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; Vaillant Arotherm Pro 7kW; 100Amp head, HA lab on mini PC

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