Hi everyone,
I have a non-smart electric Boiler that has a power consumption of about 2600Wh and works at this capacity for about 2,5 hours/day. I have it connected to a ZigBee Smart Plug and I made an automation that turns it on or off depending on the photovoltaic panels. The problem that I’m facing is that the smart plug beaks after one or two months of usage. Now I’m at the 7th smart plug. I’ve tried cheap Chinese ZigBee smart plugs of 20A (https://www.aliexpress.com/item/1005003999205172.html?spm=a2g0o.order_list.order_list_main.35.99091802Hc4div), I’ve tried TP-Link Tapo P100 smart plug, I’ve also tried some other WiFi smart plugs. They all broke. They are still connected to Home Assistant, they make the clicking sound, but they do not let the current through anymore.
Even though it might seem that it is the boiler’s fault, I’m more inclined to say that the smart plugs are of low quality and cannot handle that 2.6Kwh sustained load. Can anyone suggest a good smart plug that won’t break in this scenario? It can also be a smart relay. I would like it to be ZigBee and to provide live consumption. Thank you.
20A would have been low for my previous house’s boiler (32) but whatever they put on the label does not mean it covers that too 
An alternative could be a relay indeed, possibly you have some controls on the boiler that you may shortcut with a dry-relay. i.e. my old one had a on/off button that controlled a relay of the boiler. You could add a relay to replace the on/off…just my 2cts
You need a contactor.
Contactor - Wikipedia
The contactor itself can be controlled with a smart plug or similar but the contactor needs to control the boiler
It’s a very simple boiler. It doesn’t have any button. It only has a led and a temperature control knob. I have to open the boiler case to see if I can interfere with this knob an mount a relay in there.
I’ll have to research this contactor and its use. So does this contactor has one output (the power cord that goes to the boiler) and two inputs (one from the power grid and one from a smart plug)?
A simple search for a contactor on an online store revealed a lot of models and prices. I hoped for a simpler solution to my problem 
But, I’ll look deeper into contactors because they seem to be sturdier than a smart plug.
I agree.
Smart plugs and such are not designed for frequent switching high current or captivate loads. They use micro-relays which might have the rated current-carrying capacity to be more than sufficient for your needs, but their contacts are not capable of performing more than a couple of hundred switches at mains voltage. This is because the contacts are miniaturised and not designed for repeated high-current switching and because they do not have an ability to perform either arc-quenching or zero crossing which both help to prolong the life of the relay heads.
If you regularly need to switch high currents and cannot suppress the load beforehand, then you should not use a smart device as the switch but instead should use a electrical contactor managed by the smart device. Contactors are available in various load ratings but also in NO (normally open/off) or NC (normally closed/on) configs so that you can decide on the contactor’s uninitialised state. For a boiler you would typically choose a NO type so that the boiler is only powered when the smart device passes current to the contactor.
If you can figure out where to put a relay, these switch and measure 25A
This seems the reliable solution, but I’m loosing the metering function. I read that a contactor must be used for high currents, exceeding 15A. My boiler consumes around 12A. Maybe a smart relay is an appropriate choice.
Can’t I just cut the power cord and pass it through this relay? I think I’ll go with this relay. Thank you
Yes, that’s the trade-off.
Power monitoring would then be done by using a CT type device.
The Sonoff should be better than a small smart-plug - that is as long as Sonoff are using a good quality relay and contacts.
The sonoff has a CT clamp inside it for power monitoring
I used Shelly EM to control a properly rated contator (as fitted and verified by an electrician) and CT clamp leads back to the Shelly EM to monitor power. Some of these smart plugs are just too small to contain relays that can manage heavy currents.
Good point - the Shelly EM actually states that it has a contactor output.
https://www.shelly.cloud/en-ie/products/product-overview/em-120a
So you tried to use a TP-Link Tapo P100 rated at max 2300W to run a 2600W boiler? No wonder it fails.
Most smartplugs are only rated at 2300W and smartplugs from unregulated markets might be even less precise on this value.
Sonoff POWR3 has been suggested, but the power metering might be unnecessary here, so the Sonoff TH16 might be a better choice. It is rated to 3500W.
Sonoff might be chinese, but their products are sold by wellknown resellers in both US and EU, where the resellers can be held accountable for the products they sell and especially the bigger chains know this and do not want to risk a public scene, so use those as an indication for the product quality.
Well… I had that Tapo plug doing nothing and I’ve put it to use… for a while… a short while 
I think it was the second plug that I used, so I kinda knew what the power consumption was. But that didn’t stop me to use it . I tried it, it worked, so I left it plugged in.
Thank you for the suggestion. I like having the metering, so I think I’ll go with the Sonoff POWR3 suggested above.
That is the kind of thinking that will cause you to burn down your house with an electrical fire.
You really got lucky that just the contacts failed to close and that the whole thing didn’t catch on fire.
Is your boiler really plugged into an outlet ? Here in the UK boilers have to be hard wired into a fused connection unit
Yes, it is plugged into a regular wall socket. I really don’t know if there’s a law or some regulation to require the use of special connections for big consumers. This is how the constructor delivered the house.
It might on average, but there is usually a large spike at initial power on. That spike (over and over) is probably what’s killing your contacts.
I know that I’m resurrect this thread but someone has a real example of connection with contactor and smart plug? A schematic or picture?
I’m using for many months some ZigBee smart plug to control my espresso machine (others as boiler etc as well for electricity measure but this is what interested) and I feel little scared to use it.
@fumantsu In my country a contactor would go into your consumer / breaker box. My electrician installed it and I supplied Shelly em to control it. See post higher above