DIY Zigbee Water Heater Switch

Hi all,

I am looking to build a Zigbee switch for my water heater using a Zigbee light switch and 30A relay as the options available in my location are poor. I have seen a few examples where people have done this but the supply to the zigbee switch have been on a different circuit to the heater itself. This is not an option in my case and was hoping to power the switch from the same feed as the water heater.

My background is mechanical however I occasionally dabble with electronics when needed. Is there any reason to why i couldn’t do this?



16amp looks odd. You are in the UK, so your voltage is 240v or what?

I don’t know the rules in UK but if it was my equipment I’d put in a local disconnect at the heater, upstream of any new controls. So when the smoke comes out I won’t have to run back to the breaker. On the other hand if water is spraying out then probably wouldn’t touch the disconnect.

I’d be loathe to leave this modified circuit to someone unfamiliar upon selling the house.

Otherwise it looks like it would work, assuming “to heater” goes to the original thermostat, and grounds are installed.


Thanks for having a look. I am in NZ but we are still on 240v. The plumbing and electronics are a little different here, there is only the heating element for the hot water, no gas boiler and heater exchange. There actually is a switch on the wall with a flexible hose (with the wires inside) that runs from the wall into the front of the water heater. I plan to put the control between the wall switch and the heater so there will be an additional switch upstream. All of the thermostat controls are build into the heater so as far as the heater itself is concerned nothing has changed. I agree i probably wont be leaving the switch in place if we were to move!


So i completed the install today, all seems to be well. My power company gives us a free hour of power (off peak) per day so the heater is only going to be on during this period of time. This has effectively given us free hot water!

pretty nice to get free power.

neat dongle install. Part list would be nice for others.

Maybe you already moved it but best to get it off the ground since that is where the water will go in an emergency.


Parts list as follows

Electrical Enclosure
Zigbee/Z-Wave Switch
NC Relay (30A 230VAC for my application)
Flexible Conduit & fittings
Some 30A flex and connector blocks

I plan on raising the box a little higher but there is no point in going much more above the level where the conduit goes into the water heater; if its that high I am already in trouble! A neater job would have been to mount it onto the wall but i did have the space.