On Wed, 19 Apr 2006 11:49:33 -0700, Martin Pentreath wrote:

Hi,

I planning on descaling the DHW heat exchanger on my combi. It's an
Ariston Microgenus 27 and the rate of flow has gradually declined since
it's been installed (over three years ago). The descaling looks like an
easy enough job, and removing the heat exchanger itself is dead easy,
but before I make a complete fool of myself I've never really
understood exactly how the combi does the DHW. Do I need to drain the
boiler completely (and all the rads) or is just turning off the cold
water feed to the combi enough?

You'll need at least to isolate the primary side as well, but most boilers
have valves on the flow & return so you shouldn't have to drain the rads.