the hot water damages the hose, once you start using hot water the hose becomes really stiff and wire like when you only use cold, normal microbore is more effected by the hot/cold cycle than thermobore, thermobore stays more supple when its cold and doesnt go as cooked spaghetti like when hot, also you can use water at a higher temp with thermobore
heat loss at the brush head is mainly down to how much you have heated the water, how far you have reeled the hose out, how cold the ground is and how many times you stop and start the flow like by using a crapadapter after every window, if you stop start the flow all the time the water will only be luke warm or cold where as if you leave it running the water will be nice and warm,
or just do a dazmond and not do it correctly stop and start the flow the water is cold, turn the heat up till your melting the hose and then blame the system as rubbish and go back to cold