I find in my house where the water is hard with calcium, they last about 7 years, 10 at a pinch. Had one recently that started dripping at about 1 drip every 2 seconds. This meant the shower tray was constantly wet and if the doors were left open then the splash ended up making the toilet shower room floor wet.
The replacement valves are more expensive than throwing away the whole mixer and replacing it.
30 years? One I have has been good for 20 years now. Might be the calcium like you said. We don't have a lot of Ca. Just iron in the water.
Just stripped mine down and found it was knackered. Chalky water here just dries things out. The insert cartridges are impossible to get or stupidly expensive (more than the entire mixer tap unit which comes with one. So I bought a new (unused) one from a private seller on ebay and went for a decent quality.
The good news is they are easy to replace.
QuoteChalky water here just dries things out.
"Dries things out" sounds like elastomers. Perhaps there is a difference in design. In the good old days valve seats were metal, and were "lapped". It's much easier and cheaper just to press-in a "soft seat". And then you get different types of "soft seats". Reinforced PTFE, like stainless steel or carbon fiber reinforced, are probably the best, or something called TFM-1600. Those are more expensive. So they use a cheaper plastic. Even the good stuff eventually will get "cut" from the high velocity right before closure. Chalk grit is also bad, and some plastics will slowly swell and fail in water environments.
Also any o-rings need to be something like Viton.
I suspect mine, purchased in the early oughts likely has metal seats.
Mine had a metal seat and a ceramic disk with a bonded rubber face about.0,5mm thick. Not replaceable. The rubber on ceramic had hardened up and flaked off like cement when I tried to clean it. I looked using Google images but could not find a replacement cartridge
I managed to buy a brand new Aqualisa unit for 50 quid. They are a pretty decent brand like Grohe. Hopefully it will last 10 years. Problem is I have 4 showers. So every 2 years I am replacing a mixer