Chis,
The problem with the Steamate on hea-sensitive upholstery is that the heat sensor is located just after the heat exchanger.
When the flow through the unit is fairly constant his is not a problem.
With upholstery cleaning however, the flow tends to be intermittant, as we swap between pre-spraying etc. and extraction. When flow through the unit stops, regardless of whether the thermostatic control is suppling power to the heat element, the core has stored heat which is transfered to the water within the core. Resultantly, when flow re-commences, the water can be much hotter than the thermostat setting.
This can be overcome by having the Steamate close-coupled to the tool and by purging the over-hot water into a bucket before re-commensing the clean. Because of the time wasteage entailed, I prefer to use a Heatermate on these jobs.
John.