May not be triangular
Depends on the age of the system.

Squares, triangles and hexagons but a 4 ended key should fit anything.
( The Disappointed Caravanner of the year, Thu 18 Nov 2010, 20:46, 1 reply, 15 years ago)

Oh it's the key she was going on about ;/
I've only ever had recourse to the triangular one, across rads maybe for a 20 year period. How I've never come across the other ones is beyond me.
Rory /blog
( Light In Chains maker of the ikea sofa, Thu 18 Nov 2010, 20:51, Reply)

Depends on the age and quality of the system
If it's square it's the awful microbore stuff designed by '80's people and it won't work very well anyway.
( The Disappointed Caravanner of the year, Thu 18 Nov 2010, 20:58, Reply)