Archived Forum

Are you sure your tank is at mains pressure?

If your spare tank has an immersion heater, why not equip that with a triac switch and use Robin's multi-load sketch? When the first immersion heater cuts out on its thermostat, the second will automatically take over the load. Alternatively, if you pipe the tanks in parallel, with a bit of ingenuity in the sketch you can fire the triacs alternately, thereby heating the two tanks evenly without relying on convection to share the heat. I've done this on a 3-tank system - it works under simulated conditions but isn't yet installed.

thanks for the thoughts Robert.

My tank is an unvented mains pressure system. I have a spare conventional vented tank so I was thinking about a changeover valve that would allow me to switch between the two.

I think I see what you're trying to do. So your real problem isn't getting the spare energy into the water, it's getting the water out to make use of it!  A very quick search found this one - good to 10 bar but it's pricey. I suspect the pressure limit was a result of the "solenoid" bit, a motorised valve will be less sensitive to the system pressure. You probably need to make sure that you don't back feed the low pressure tank while the valve is travelling, so you might end up with two, two-port valves and an electrical interlock between them.

My system has two immersion tanks but the second tank contains 'radiator water' not DHW. When tank two is hot enough a three port valve is opened to allow the very hot 'radiator water' to pass through the heat exchanger in tank 1.

In my case both tanks are vented but because the two fluids are kept apart it should be possible to pressurise one of the tanks.

The net result is a much higher diverted energy limit. 16kWh today :)