cosydays Open the app

For Octopus Cosy heat-pump owners

Warm home, lower bills, and proof the change helped.

Cosydays watches your Octopus Cosy heat pump, lets you adjust it from your phone, and then checks — against the weather — whether what you changed actually made a difference.

Open the app See what it does

Independent companion app. Not affiliated with or endorsed by Octopus Energy.

Heating · Auto Live
21 ° NOW 20.4°

Warm and running efficiently.

Cost today £1.84
COP · 7 days 3.62+0.40
Illustrative. Your own figures will differ.

What it does

Four jobs, one app.

A thermostat you happen to be able to analyse — not a report you can also poke.

  • Monitor Live today

    Live status, flow and return temperatures, COP and what today has cost you — collected continuously, not only while the app is open.

  • Control In build

    Setpoint, schedule, boost, hot water and zones. Every write is clamped server-side to the range your pump reports, and refused outright if it does not report one.

  • Understand Live today

    History by day, week, month and year, with cost alongside efficiency. Every chart carries labelled axes with units and an exact-value tooltip.

  • Prove In build

    Log the change you made, then get a verdict on whether it helped — with the weather held constant, so a mild week cannot take the credit.

The loop

Analyse, tweak, prove.

Most heat-pump advice stops at the tweak. The interesting part is what happened next.

  1. 01

    Analyse

    Cosydays reads your own run data and says, in plain English, what is costing you — a flow temperature set higher than it needs to be, short cycling, hot water eating the bill.

  2. 02

    Tweak

    Make one change, from the app or from the pump itself, and log it. One change at a time is the whole trick — two at once and neither can be attributed.

  3. 03

    Prove

    Once enough comparable weather has passed, you get a verdict: it helped by this much, it made no measurable difference, or it cost you. Then you keep it or undo it.

Weather-honest comparison

A mild week is not an improvement.

Compare this week against last week and a heat pump will almost always look better or worse for reasons that have nothing to do with you. Cosydays matches periods on how cold it actually was — heating degree days and outdoor temperature bands — before it will call anything a change.

When there is not yet enough comparable weather to be sure, it says so rather than inventing a verdict.

Raw comparison −18%

Looks like a win. It was four degrees milder.

Weather-matched −4%

The part that was actually you.

Illustrative figures.

Straight answers

The things worth knowing up front.

Is this made by Octopus Energy?
No. Cosydays is an independent companion app and is not affiliated with or endorsed by Octopus Energy. It uses their publicly available API with your permission.
Do I need an Octopus Cosy heat pump?
Yes. Cosydays reads and controls the Cosy heat pump through the Octopus API, so it only works if that is what you have and your account can see it.
Where does my data live?
On our servers, and that is deliberate. Weather-matched verdicts, year-on-year history and comparison against similar homes need collection that carries on when your phone is asleep — none of it can be done on the device alone. Your Octopus credentials are stored for that collection and are never shared or sold.
Will it change my heating without asking?
No. Nothing is written to your pump unless you ask for it. Every write is clamped server-side to the range the pump itself reports as allowed, and if the API does not return a range the write is refused rather than guessed. Controls pause during an outage so nothing is sent into the void.
How does comparing against other homes work?
It is opt-in and off by default. Only anonymised rollups are shared — efficiency, cost, cycles, set-temperature band, the outward half of your postcode and unit size. Never your API key, name, address or full postcode. A cohort only renders once at least twenty homes match, and you can leave and delete your contribution at any time.
What does it cost?
Nothing while it is in build. Paid plans are planned for later; nothing is charged today and you will not be billed without choosing to be.
How finished is it?
Monitoring and history are live today. Control, the analyse–tweak–prove loop and similar-homes benchmarking are in build — they are marked In build above so you know what you are signing up to.

See how yours is actually running.

Connect your Octopus account and Cosydays starts collecting from the first reading.

Open the app