I started using my used devere 10x8 recently when two bulbs blew. There was a little flash ( which I could see from the small amount of light spilling from around the carrier onto the wall) and the two right side LEDs went out, showing that those two bulbs had gone. I inspected them and they had blown. I replaced them and within a few prints the left two bulbs went. This time there was no flash, the light source just dimmed and the LEDs went out. I have replaceed these two so there are now 4 new bulbs in the head.

Being used to smaller enlargers with less bulbs and having only one bulb go in 3 years, can you help on the following:

I once heard that all bulbs should be replaced when one fails. Is this true and if so, why?

Could it be that there was some form of surge which blew a bulb in a sudden way (flash) taking another with it immediately due to an increase in load and damaging the other two, which then shortly after gave up the ghost? (I hope so)

Could there be a more serious problem? (I hope not)

I have made a few prints and all seems well for now, but heck, the bulbs cost a fortune and if I have a bulb eating enlarger it could hurt a lot.