To start off, I absolutely hate idea behind thermostatic mixing valve, but that's not a question.
The water in my house runs hot for about 10 minutes and then turns icy cold, and I have to turn it off and wait for an hour for the hot water to come back for ten minutes again. I assumed problem was with my boiler. So I called a repairman and he told me that boiler is functioning properly and that issue is with my thermostatic mixing valve. He explained to me that they have to be replaced once every 3 years or so and told me that it will cost 400$ to do so. His explanation was that government in Canada uses chemicals that break thermostatic mixing valve.
I am extremely broke, and can't dish out 400$, however I have kids that need to take a bath, and having hot water for only 10 minutes makes it really hard. Does my thermostatic mixing valve need replacing or is there any way I can fix this issue with water turning cold after ten minutes?