Hello everyone, first time here and I hope someone can help me with some information.

In my home I have a hot water heating system powered by a Viessmann Vitodens 333 which is a gas fired condensing boiler. We added an living room extension onto the house 6 years ago and the heating contractor ran PEX tubing to three radiators that are embedded in the floor of the extension. For 6 years the system functioned without a problem.

About 8 months ago we had a leak from the PEX tubing and after opening the floor we saw that it had a 4 cm split in it. The heating contractor who installed the system originally cut it out and spliced a new section into tubing. At the time he claimed that the material failure was due to the weather having been so cold for 2 weeks. I didn't buy the argument because there is hot water circulating through the system at all times, particularly when the temperature is under 0 C.

Now, a leak has developed in different section of tubing in the same extension. They haven't opened it up yet but I'm sure it will be the same problem as with the first leak. Now, the same heating contractor is saying that the temperature from the Viessmann boiler is too hot, i.e., when the boiler must heat water there is a surge in the heating system and this weakens the PEX and therefore causes a leak.

I'm sure you can understand my scepticism. I wish I could tell you more details about the type of tubing but all I have seen is that it is while, about 15-20 cm in diameter, and has an aluminum lining. By the way, we live in Switzerland if that helps.

My question is, does this type of tubing rupture under normal operating conditions? And, if it does, what are the possible reasons for that happening.