Why does the high voltage side of transformers tend to burn out first?

[Averagesupernova]

It's quite simple. Folks have gotten used to the fact that most consumer items are not built to last and take the abuse and continue to work like a drone flying to Mars. It is accepted that water heaters get tossed every few years and home heating systems are not far behind. We all know residential furnaces could be built to last a very very long time. The cost of such a furnace would be much higher than what we have now. I can't say I like it this way, but in some cases it has advantages. My high efficiency gas furnace has failed due to a leaky condensate pan and a plugged orifice that serves to carry the flame across to all four burners. None of that was electronics related and I cannot complain other than about the dummies that tried to sell me a new furnace because they were too stupid to realize what was happening when it went into safety lockout because the flame was not being carried from the first burner next to the igniter all the way across to the fourth burner where the flame sensor is mounted.
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If we want to have equipment that lasts for half a century, then we need people that understand the equipment better than the schmucks that attempt to service the equipment now and throw their hands up and say: I guess you need a new one. It doesn't matter how well something is built, when it has some mechanical parts, it will need service of some kind in 50 years.
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So to boil it down to why are these transformers failing, it can be simply said because the manufacturers can get away with it.

 

[sophiecentaur]

So to boil it down to why are these transformers failing, it can be simply said because the manufacturers can get away with it.

Maybe it's not as the repair man was implying. He may have found many other faulty components and the few transformers that he actually examined in detail had this particular problem. Not a regular enough fault for the makers to sort out the problem, perhaps.

 

[Averagesupernova]

Maybe it's not as the repair man was implying. He may have found many other faulty components and the few transformers that he actually examined in detail had this particular problem. Not a regular enough fault for the makers to sort out the problem, perhaps.

Could be. I will say that my parents oil burner has a blade style fuse on the circuit board. It has blown several times due to an intermittent problem on the outdoor unit (air to air heat pump). It is a dual fuel system. Prior to the intermittent issue, that circuit board was replaced due to an unrelated issue. The fuse is on the low voltage control side. It's a pretty efficient setup, but it has not been without trouble.