Modify your routine. Put water in the machine first, say a couple of buckets. Keep an eye on it while you do the other things like pre-vac, spray, agitate, adding an extra bucket as the water reaches it's optimum temperature. Whilst you are rinsing, rather than let the tank empty, keep on topping it up, that way you'll always have enough hot water available.
It should be noted that most water pumps don't like high temps. Typically 60C is the max. Some may be even 50C.
I don't use a heater, just hand hot from the tap or even cold. The right system and procedures can reduce or often remove the need for higher temperatures.
Safe and happy cleaning
Ken