How a Tallinn CEO moved his water boiler to the three cheapest Nord Pool hours of the day
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If you pay for electricity at the Nord Pool exchange price in Estonia, you already know the game: the same kilowatt-hour can cost five times more at 18:00 than at 03:00. A water boiler is the easiest appliance to move into the cheap hours, because hot water stores energy. This is the story of one customer in Tallinn who bought a GPO Smart Plug for exactly that job, hit two setup traps, and ended the same day with a boiler that heats only in the three cheapest hours.
The customer's problem
The customer, the CEO of a medical-devices company in Tallinn, connected his electric water boiler to the plug and activated Cheap Mode with "Working hours = 3". The app showed Nord Pool prices correctly, but the boiler did not heat during the cheapest hours. His message was blunt and fair: why does such a basic function have to be so complicated? He suggested a two-control design: one switch "automatic Nord Pool control ON/OFF" and one field "number of cheapest hours per day".
What we did
His screenshots showed two settings that cancelled each other out. First, "Apply for devices" was set to "Turn off": that field defines what the plug does during the selected hours, so it was switching the boiler off in the three cheapest hours, the opposite of what he wanted. Second, the plug's base state was OFF. A plug that is switched off stays off; the schedule never turns a switched-off plug on. The correct standby state is ON with Manual power ratio at 0%: powered, delivering nothing, ready for Cheap Mode to raise it to 100%.
The fix took one reply: plug ON → Manual 0% → Cheap Mode → Working hours 3 → Apply for devices: ON – 100% → Activate. Then one Deactivate → Activate cycle to push the recalculated schedule to the plug immediately. (A second issue appeared minutes later — the app would not hold 0% — and that one was ours; see the firmware-fix case.) His last message that day: "Thanks, now it's working."
Benefit for the customer
The boiler now runs for three hours a day, always in that day's cheapest 15-minute intervals, without anyone watching the price table. For reference, the example on our product page: a 2 kW boiler running in daytime hours costs around €250 a year; shifted to the cheapest night hours the same hot water costs around €75, a difference of roughly €175 a year at the price spread we used for that calculation. Your numbers depend on your tariff, tank size and the year's price curve.
Technology used
GPO Smart Plug, 16 A / 3 kW, Wi-Fi and Bluetooth. Cheap Mode reads the Nord Pool day-ahead price for Estonia (also Latvia, Lithuania, Finland), works in 15-minute intervals and recalculates the schedule every day when new prices are published. The schedule is delivered to the plug over the internet; if the connection drops, the plug keeps the last schedule and resyncs when it is back. Consumption is logged per interval, so the next day you can see in Statistics that energy was used exactly inside the highlighted windows and nowhere else. No subscription, no third-party cloud (no Pörssäri, no IFTTT), everything in the free GPO Home app.
Improvements and know-how
This conversation changed three things. First, the one rule most people miss is now written down as a setup guide (the full version is in our Latvian base-state guide): OFF overrides Cheap Mode, the base state must be ON at 0%. Second, in-app explanations for "Apply for devices" and a warning when the plug's base state would block the schedule went into the development plan. Third, the two-control layout the customer sketched ("automatic price control ON/OFF" plus "cheapest hours per day") is now the target design for the Cheap Mode screen.
What's next
The customer's boiler was the first appliance. The same plug can run floor heating, a towel dryer or an EV charger on the same logic, and one plug per appliance is the normal way to scale (2 plugs = 5% off in the cart, free parcel-machine delivery from €60). On our side, the next step is the simplified Cheap Mode screen and a "next ON window" indicator so nobody has to ask whether the schedule is active.
FAQ
Why doesn't my boiler heat even though Cheap Mode is active? Almost always because the plug is switched OFF (it must be ON at Manual 0%) or because "Apply for devices" is set to "Turn off" instead of "ON – 100%".
How many hours should I set for a boiler? Start with the time a full tank needs from cold, typically 2–3 hours for an 80 L / 2 kW boiler, and add an hour if you run short.
Will the hours be consecutive? Rarely. The cheapest hours of a day usually come in two or three blocks, and that is correct behaviour.
Where to get it
GPO Smart Plug — €35, 2-year warranty, Omniva/SmartPosti delivery in 1–3 working days: GPO Smart Plug for spot price automation.