What's this part ?

[pmax]

Found this 'springy' metal loop stuck above the heat exchanger on the sc.
It's about half a foot in diameter.

Anyone recognize it ?

[Tidybuoy]

my guess is that it is a wire from the heater lever to the flapper box. it may have been replaced and the old wire was left there. They are usually contained in a plastic sheathing.

That's my guess.

[Caledonian]

Or it could be the reinforcing wire from the heater hose?

[gamin]

I'm going with reinforcing wire from heater hose.

[Steam Driver]

Definitely some reinforcing wire from the heater hose!

[pmax]

Right on...

Checking the maīntenance records, the heater hose was replaced in 96