What a blight! A curse on the lawyers who forced these things to be
mandatory.
Mine has seized up, so the water is only 40 Celcius with the screw on
maximum (supposedly 50). The plumbing company that installed it went
bankrupt. I complained to the manufacturer, and just got a robot reply
that dirty water is the usual cause of failure and they should be
replaced every 5 years anyway.
A gasfitter friend told me to get another brand, which is rather expensive.
So I removed the tempering valve, and stuffed some neutral cure silicone
into the cold intake. I left it in the sun for 8 hours, so that it was firm,
then put it back on the water heater.
Hot water once more!