Thanks for replying!
Would that be 'safe' as far as legionnaires or damage to the unit? If it is, then what would be a good amount of time/temperature for the monthly heat-up?
We have an unvented cylinder with a Horstmann Electronic 7 timer. The cylinder only serves a wet room which is very rarely used. The rest of the house is served by a Vaillant combi boiler.
The timer on the cylinder is set to heat up water 3 times per 24 hours, which I think it is the default...