When I fitted a rad in the porch, in 2005, I drained the system, and
refilled with a gallon of X100, which is what the original installer
used in 2002.

ISTR that it should be renewed every 5 years ?

Just fired up the CH (following the thread on first use of CH this
season !), so it'll be giving the circuit a good ol' mix up.

Is it really as straight forward as opening the drain valve (outside
the house) and then taking the bleed valve of my towel radiator,
pouring the stuff in, and filling with water ?

On a related note, I noticed the pressure dial was reading 1bar, yet I
know I left it at 2bar, back in March. Is some leakage or pressure
drop, normal. The installer showed me how to open a small valve to top
the pressure up, but never mentioned what was normal or not.

Jethro wrote:
When I fitted a rad in the porch, in 2005, I drained the system, and
refilled with a gallon of X100, which is what the original installer
used in 2002.

ISTR that it should be renewed every 5 years ?

Just fired up the CH (following the thread on first use of CH this
season !), so it'll be giving the circuit a good ol' mix up.

Is it really as straight forward as opening the drain valve (outside
the house) and then taking the bleed valve of my towel radiator,
pouring the stuff in, and filling with water ?

Yes.

On a related note, I noticed the pressure dial was reading 1bar, yet I
know I left it at 2bar, back in March. Is some leakage or pressure
drop, normal. The installer showed me how to open a small valve to top
the pressure up, but never mentioned what was normal or not.

It could be a small leak. Check aroung all the valves and blled valves for
any weeping.

--
Adam