What pressure will the Heat 'n' run take and what pressure is your pump?
If you have 300psi hose, it may be necessary to upgrade to 3000psi. Even @ 100psi and very hot water, a 300 hose is more liable to blow fittings.
On longer hose runs, move the heater closer to the wand.
Be careful not to heat set hose pressure marks in customers carpets, esp. polyprop.
Safe and happy cleaning

Ken