Problem with Nest Heatlink

Supernintento Chalmers

The problem is with the hot water control on the heatlink. AFAIK the relay should close across terminals 5 and 6 when hot water is turned on at the stat. The problem here is that this relay is closing by itself. If I kill power to the heatlink, the relay opens, but at random times the relay is getting closed and refusing to open, regardless of what you do with the stat, etc.

Supernintento Chalmers

This may be the cause.
https://nest.com/uk/support/article/How-does-the-Nest-Thermostat-help-prevent-Legionella-bacteria