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!

In article ,
writes:
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!

Probably just wanted descaling. When the hot water mixes with cold,
the cold drops scale out onto the surrounding surfaces as it's
heated up. Happens in shower mixing valves too (although to a lesser
degree, as they aren't normally set to 50C).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Friday, June 26, 2015 at 4:58:55 PM UTC+8, wrote:
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!

I think you are lucky that it worked. I fitted a stopcock in the cold line to get extra-hot water. However, the thermostat still expands to choke the hot water and I only got a trickle, barely enough for a water-saving shower head.
Thus you have to remove the innards of the TMV so hot water flows freely. It is spring loaded, so bits may fly out, but if you want to disable it forever, that will not worry you.