Water heater with a plug: Shelly smart plug
If your water heater plugs into a socket, you need no relay and no contactor: a Shelly smart plug goes between the heater and the socket. No electrician needed, about 10 minutes.
A short video of this guide is coming.
Check the power
Check the power on the heater's rating plate. The Shelly Plus Plug S and Plug S Gen3 handle at most 2500 W; most 50–80 litre plug-in heaters are 1500–2000 W, which is fine. Above 2500 W do not use a plug: you need hard wiring and a Shelly Pro 1PM, fitted by an electrician.
The socket
Plug it straight into the wall socket, not into an extension lead or a power strip. If the socket or plug is warm, brownish or loose, have an electrician replace it first: the heater draws full current for hours.
Set it up in the app
Plug it in, add it in the Shelly Smart Control app, connect it to Wi-Fi and install the update. Settings → Power-on state: "Off" (after a power cut it should not switch on by itself).
Plug the heater in
Plug the heater into the Shelly plug. The heater keeps its own thermostat and temperature control; leave it on: the plug only gives or takes power, the heater still keeps the water temperature.
Electronic heater?
If the heater has a display or push-button control, test it: switch the plug off and on again in the app. If the heater starts heating again by itself, it works. If it stays on standby waiting for a button press, a plug cannot control it.
Link it
Linking works as for the relay: paste the address from your account page into the plug's Outbound WebSocket setting. The linking guide has the steps.
