You're best off with Opto or Crydom SSRs. And make sure they are properly heatsinked to something (with thermal paste!).
Is the one that failed just switching an immersion, or are you switching motors too?
In the case of motors, because they are reactive loads you need a snubber in the load circuit to prevent damage to the SSR output stage. Some SSRs include a snubber but some don't, and those are only good for resistive loads like immersion elements.
Think of it like this, when the motor is driven, it it taking power, but when you switch it off it is still spinning and starts to generate power as it winds down (much like an IMAG generator). This power has to go somewhere and your poor SSR is where it ends up - pop!
