Hot tap water
I was experimenting with my Panasonic (Gorenje) washing machine, on the supposed 50 minute 'Quick Wash' cycle. A few days ago, with cold tap water, for a smallish cottons load at 40°C, it got up to the heady heights of... 27°C. I wasn't amused.
Today, I decided to run another small load, on the same programme... but this time I decided to fill the machine to the bottom rim of the drum, with - don't laugh - saucepans of hot tap water at about 55°C, directly tipped into the drum. I added powder directly to the hot water in the drum, swished it about for a few seconds, added the laundry, set the programme temperature to 60°C, and lo and behold - a temperature of 64°C was achieved. Queer old difference.