My luck sucks with solid state relays. And since I am not a great believer in luck, I'm thinking I do something that kills them. I can't imagine what though.

My streak of bad luck started with releco relays like this one.

we were using 48V versions. Originally these were the type that switched with 120V, but later we used the kind switched with 24V.

We also had issue with high amp relays from omega that also switched 120V AC from a 24VDC coil.

Since the failure rate is high, we are planning to switch again.

So: What can cause solid state relays to fail? and way more importantly, what inexpensive way is there to detect and subdue a failure, because each and every failure was a closed circuit! So heaters go ON when a relay fails. That is bad news!