Harry Bloomfield submitted this idea :
on 30/04/2018, Brian Gaff supposed :
Or perhaps it is via a thyristor and the break in the circuit required to
snap the scr out of conduction is not happening due to any number of things
in the circuit.

The OP mentioned it being a relay in his text, but called it an SCR in the
subject line.

Would it not have been a triac anyway, passing ac?