The Heating Hub estimates that you can save another 5-10% if you have a Worcester, Vaillant or Ideal combi boiler by turning ... For this reason, don't set the flow temperature lower than 65°C without ...

His clip is specifically about Vaillant products, but the plumber says the same changes can be made to combi-boilers ... set it at about 50 degrees, then run their bath tap and test the temperature.