Boiler isn't heating regularly

Hey all,

Got a call from mom last night. Her downstairs tenant is a peice of work and complains that he isn't getting heat. Might be BS, not sure.

I'll get more info and pics but tenant is on his own hot water boiler. When I took a look at it, stack was hot and circ pump was hot. Tenant claims that at random times the boiler stops working.

Mom had a plumber in who told her she needed a new heat exchanger, but manually lit the pilot light just to get the boiler back on. That's a real head scratcher of a statement to me.

Is the red light on the box indicative of a problem? What other details should I gather to help troubleshoot?