We are trying to replace an aqualisa thermostatic cartridge
The screws on the old knee are badly corroded and impossible to get out, what can we do? We've tried lubrication, vinegar, lemon juice and drill bits for stuck screws. Nothing is working. Will we have to cut into the cartridge somehow?
Spray ww40 .Spray any limescale wait until clean and unscrew
Hi if I can't open the screws you will have to work around and take the body out some tiles will need removed , and recommend to replace whit new body and Cartige as the old one will be compromised if you try to force the screws out
Most of times screw thereds will get damage
Depending on the cost of the shower unit vs the cost of the cartridge and the time it would take to replace it, we would often recommend replacing the unit instead as this would be more cost effective both for time and money.
Anything you drill into you risk causing more damage and of course you must ensure you then have replacement screws to seal the unit properly and fully. Otherwise you will get a leak.
Hope this helps
Shower cartridge can be replaced only by someone with a good knowledge about showers and plumbing itself
Try an impact driver drill or heat