Name this bolt, please.

[John Delacour]

At 13:45 -0400 23/3/08, Kerry wrote:

>That's an intriguing statement - what kind of heating do you have, how do
>you adjust the pressure on it (not sure what that means, unless it's
>steam?), and what does the plumber have to do with it?

Just a "combi" boiler with the central heating pressurised to about 1 
atmosphere, which I suppose is pretty normal.  Over time the pressure 
drops and one has to raise it by opening the system to the main.  In 
the old days you'd have a sturdy brass cock to turn open until the 
pressure was right and then close.  This is now forbidden and is 
replaced with a slotted screw, which one has first to find, then get 
a screwdriver that's long enough to get past the pipes that are in 
the way.  You then have to hold the tip of the screwdriver in the 
slot so that it doesn't wander, while tuning the rather stiff screw a 
quarter of a turn, and back again when you're finished.  If you don't 
fully close it, which is easily done, then slowly the pressure in the 
system will rise to mains pressure, probably leading to leaks and 
even bursting the heat-exchanger and flooding the house.  No doubt if 
I read the regulations I'd discover that I ought to take nil by mouth 
for 5 hours before the operation and wear goggles and a safety belt 
to British Standard 5908-b.

JD