Lime scale on the spray head K4 Grohe - Grohe 32.074.KD0 K4 Prep Sink Single-Spray Pull-Out Kitchen Faucet - Stainl

SOURCE: Grohe 32 071 K4 spewing water from single vale or tube under sink

There should be an o-ring on the mating surfaces of the hose and the faucet that my be missing.  It could also me that the big washer in side of the faucet (under the cartridge) has been shifted.  
I doubt it is the cartridge itself, always try the cheap ideas first.

SOURCE: how to install supply lines for Grohe k4 faucet

I hope this helps.
Step11Turn off the water supply. You'll find a shut-off valve under your kitchen sink. Once the water is turned off, open up the kitchen faucets to allow the water remaining in the pipes to drain way. Step2Catch the drips by placing a bucket under the hot water supply line, located on the left side of your sink. Even a minimum of water can cause a mess and be potentially damaging. Step3Use a wrench to remove the compression nut that secures the hot water supply line. Let the disconnected section fall into the bucket. Use the wrench to loosen and remove the nut at the other end of the line and remove it as well. Step4Repeat Steps 2 and 3 for the cold water supply line. Step5Replace the cold water supply line. Hand-tighten the nuts on both ends, then use the wrench to tighten the nuts completely. Repeat the process with the hot water supply line. Step6Turn on the water supply and test for leaks

Rod Wallberg

• 494 Answers
• Posted on Feb 14, 2010

SOURCE: installed a grohe k4 faucet and it will not

Could be hung up if this has a weight to pull the hose back........