Draining and refilling the whole system regularly would be beyond my wife. I was thinking that if the CH was antifreezed it would be quite simple for her to switch off boiler & immersion, close mains water stopcock and drain DHW cylinder (thus dumping contents of storage tank as well). On next return reverse the process. She could cope with this.
The only pratfalls that I can think of are any effect anti-freeze might have on system components or copper and the propensity for anti-freeze to find potential leaks/weak spots. Is there something I haven't thought of?
Many thanks, and best wishes to all for 2010.