Help..with The Boiler

Hello! We have a boiler Tesi 80l at about 4-5 years. It is used constantly and is turned off only when no one is at home. It used to work normally. Sometimes it happens that the relay burns out (I think it's the heater.) And my father always changed it. But a few months ago there was a problem in the pipes of the unit. We were transferred to another water supply and we did not have water for 1-2 days, which was a nightmare. Then it turned out that the plumbing had left some papers with which to dry. And they had blocked the pipes, there was no pressure .. They came to blow the pipes, but it was not quite right, because there was not enough pressure and the boiler was cracking .. Then they came again and it started working. But my mother made my dad see if there were any of those papers in the boiler. He checked and said no .. After 2-3 months it happened that the switch from which the device is turned off and on does not work, as well as the relay .. My father bought new ones and replaced them .. However, this is where the problem started .. The degrees to which he set it were either 65 or 70. The water started to heat up a lot, it was too hot .. The arrow usually pointed to 80 degrees. When it was used often by the constant switching on and off, it went on and on. My father used to say that this had nothing to do with the actual temperature, but I could see that the boiler itself (especially upstairs, where there is hot water and the arrow) was very hot .. And since then I always worry and decide when to turn it off so that it cools down and the arrow goes at least to 60 .. Abe, I'm scared .. Yesterday my dad and I came home from the village and he came in to take a bath, but said he didn't want to turn off the relay. Change it and say that (what you took out) has started to melt (a small part of it, not the whole) ..