Possible Clues:

• Possible source of steam bloke heard
• Water heater, nasty grey, seen around Home Counties
• 'Hot water's here!', said the bloke
• It regularly blows its top
• Yes, it's into Reginald back there to get one into hot water
• Steaming spring
• Heard bloke spout
• A spring sending up columns of hot water
• Yellowstone feature
• Sound fellow - though quite a spouter!