No one's ever died from Legionaires in a domestic setting in UK - The turnover of water doesn't let 'L' propagate - If you were worried, you could set an alarm to really heat up the water once a fortnight/month on immersion or buy a timed immersion to do that for you.
The slight downside, is the...
Heard my heating go 'on' around 4am today.. looked on phone (thinking the kids have worked out how to bypass the lock on Wiser TRV..) and see that 'reduced/target temp' of 14 had been hit and that triggered boiler.. It's now down to 12..