Mike Halmarack wrote:

One thing leads to another.
The management company of our blocks of flats sent around some
documents which included the warning that stagnant water in pipes
above a certain temperature may harbour dangerous bacteria, namely
Legionella.
Since I got a dose of Legionella a few years back in Portugal my wife
freaked.

We don't use this hot water system as the shower is an electric power
shower.
So, I turned off the main feed to the fortic tank and drained down the
via the hot taps in kitchen and bathroom.

This morning there is much water in the airing cupboard and a steady
drip coming from the bottom of the fortic tank.

Is a drain down of the tank itself using the drain cock on the side
the probable best solution?

I can't answer the question, but the Legionella problem is *prevented*
by keeping stored water *above* 60 deg C, and regularly running water at
this temperature through the pipes. Provided your hot water system runs
well above 60 deg C regularly it is not a significant risk.
--

Roger Hayter