Is there an off the shelf component that will let me sense when a ground level hot water tank is full (supplied by heat on demand boiler) and shut the supply off?

The idea is that then a booster pump will push the water to the bathroom upstairs for high pressure / flowrate.

Here's a picture of what I'm thinking of doing;

http://img27.imageshack.us/img27/2140/39052854.png

It's important to note that the hot storage tank is being filled by the boiler (not a cold tank) and that the top of it must be open to the air so the pump can suck the water out the tank rather thank trying to suck it through the boilers heat exchanger.

John, April 2009

Not really sure what your after but a boiler doesnt fill a cylinder it heats it up indirectly so there will be a coil inside the cylinder. Its either filled by a cold tank in loft or from mains water but this would be unvented and give you mains pressure out of your taps. A pump can be fitted to the hot supply to your taps as long as its not mains pressure and the boiler will only heat the tank when needed as long as you have controls for this such as a cylinder stat. the boilers heate exchanger contains the water which travels around your rads and this should never mix with your tap water.

gg, April 2009

Having it refill from the boilers DHW would mean it came back up to temperature much quicker - was my thinking. Instead of having to wait for the immersion / coil to warm it up, the boilers exchanger would do it much quicker.

John, April 2009

Okay, I thought of an easier solution to this. To not bother connecting them to the boiler for DHW and to just have it heat them indirectly with the coils and an immersion in a cold tank setup. Although, I would still prefer to have it topped up with hot water by the boiler. I realised that what I'm looking for is basically a float valve for a hot water tank

John, April 2009