Pulsacoil 2000 Burnt Out Relay

Is it common for these relays to burn out?

Got a call to one and the customer suspected the relay was the fault because it was replaced 2 years ago. So he bought one to be fitted. Turned up to fit it but the relay was welded to the base and so now needs a new base installing.

No problem to do that but cannot find any info has to why this would happen. Would a Rod Thermostat failure cause this?

There is a possibility the base was damaged 2 years ago when the last relay burnt out and this led to over heating due to possibly loose connections in the relay base but the 2 years time frame makes me think that is unlikely, though possible.

If it is a rod thermostat failure that caused the last one to fail then again lasting 2 years operation seems also unlikely. My understanding is that if the rod thermostat is faulty (stuck on) then the overheat stat will be the thing working to operate the boiler temp, but temp in boiler not getting to the point where the rod thermostat safety trips.

But even with a fault The relay is rated 30A and the Immersion Heater is 3KW so even at full load the relay should not be burning out?

Next time I visit I can check the rod thermostat but interested to know if there was a a known reason for this type of failure.