Gas control valve problem

[Graham]

I had the gas-valve in my thirty-year-old Glow-warm central heating boiler replaced recently

and out of curiosity I dismantled the old one.

I was surprised to find that it was packed with this crystalline debris.

I know the picture isn't very clear, but the gas main side is on the right, and it seems to me

that the contamination has entered via the gas supply.

Incidentally, there are no other gas appliances in the house.

Can anyone enlighten me as to what has caused this?

Graham.

[Ed Sirett]

This may be sulphidation I dunno whether this is CuS or FeS debris. Also some sorts of grease (even the correct one for gas taps) can form a find grey dust on contact with gas, but this looks more gritty.

Since it took 30 years to get this bad you might as well not bother about it.