Kitchen sink cutoff not working - advice please?!

[Aliris19]

Hi all - I am a novice* to say the least. In preparation for changing out the water cartridge on a Grohe ladylux kitchen sink faucet, I twisted the hot and cold water cutoffs to the off position ... and discover that while the cold seems to work the hot does not. That is, hot water still comes through the faucet.

Yikes what do I do now?

I noticed the valve does creek and squeek so I did use some WD40. It's a little less creaky sounding but no change in water flow. There's a screw in the center of the oval caps, but that seems to move along with the caps so I don't think, say, anything is snapped off at that point. It just occurred to me maybe the caps are 90-degrees to off, but no.... twisting them all the way to the right still doesn't get the hot to stop flowing, nor does twisting it the left.

Am I right that some actual cutoff valve or constrictor inside the pipe must be frozen shut and not closing?

Do I have to shut off the water main to the house, and somehow unscrew this piece of pipe and replace it with another valve? Is that a really hard job?

Thanks for your thoughts.

(*I did install a toilet and I did fix my washing machine so not 100% novice but definitely intimidated by removing actual big, metal pipes filled with water....)

 

[Fitter30]

Shut off the main water supply, open some valves and drain system down. Valve has to be replaced. Might want to wait till tomorrow when stores are open if you need anything.

 

[Sponsor]

 

[Aliris19]

Great, yes; thanks fitter30. After writing this I watched some youtube videos and it seems fairly straight-forward. Also someone suggested the possibility of coaxing the sticking phlange with hot water and WD40 and patience, though on a hot water line this is evidently less likely to work. I may try; nothing to lose and I have to go look at what's needed anyway. I don't want to have to cut the pipe for sure. I'll try to determine if this is doable just hanging out the part. It's just 5 years old..... tia.