Following on from an earlier post about a pressure reducing valve on a megaflo cylinder, I've decided to remove the cartridge and clean out the filter.
Guess what - it won't unscrew, and seems to be stuck fast with limescale. Here's a pic:
So the question is: what's the best way to tackle this? I assume plus-gas and WD40 are not a good idea because this is connected to the potable water supply. Would it be worth using some sort of descaling cleaner to remove the limescale, or wouldn't that get down into the threads?
I'm using a 12" adjustable spanner, so one option is to use a longer one - like a big set of stilsons, but I'm worried about putting too much stress on the surrounding pipework.