Shower cartridge removal - nut won't budge

[steviep43]

Morning all

I've had a dripping shower for a year or so - a Grohe Grohtherm 3000. Plumber came and replaced the hot/cold cartridge but it made no difference so I'm assuming it's the mixer cartridge that has the leak. Although I've told the plumber he's not responding so I thought I'd look myself. The mixer cartridge was caked in limescale so I have soaked and soaked it in a rag drenched in white vinegar which has dissolved the visible limescale but the nut won't budge to remove it. I've also sprayed it in WD40 several times and left it but it looks almost like it's fused - see the pic (note I normally remove all the casing and cover but sig other wanted to shower so it's a quick snap). Any suggestions please other than finding a different plumber which is what I will do next!

Thanks

Steve

 

[blup]

Maybe a heat gun used carefully would help, or the longest handled wrench you can get which will significantly increase leverage. But be careful you don't damage or cause pipes behind to leak.

 

[oldbuffer]

1. I'd suggest first step is to remove the round chrome shroud and check whether there is a grub screw in the brass holding the cartridge in place. If there is and you force it with a spanner, you stand a very good chance of wrecking the shower.
2. Have a look at https://www.showerspares.com/grohe_shower_spares/grohe_all/grohe_grohtherm_3000_19663_000_19663_000/