Lot lovely area been to St Sulpice several times.
From what i can see from the pictures, blimey what a mess. But here goes try to make some sense of it all, mains unvented hw cylinder, that's what the blue expansion vessel is for. The other red one is for your central heating circuit. Sorry if you already know this. Under UK G3 rules it would appear that the safety release devices are not installed as per G3 requirement, these are all for safety . You can see the cold composite vale body (large black shroud) has a pressure relief that tees into pipe running across top of cylinder meets another pressure relief valve before it discharges into tundish (Not good).
As you see on last picture there is a cylinder stat albeit not as per G3 regs this should have a electrical safety cut out which kicks in if thermostat fails, which would normally be combined with the cut out correctly called Combined cylinder thermostat and `ECO (Energy cut out). You have a standard thermostat very basic, not suitable for this system really. The valve under the blue vessel would control yr hot water temp and timings as to when to come on and off (This is likely where temperature issue lies), as for the motorised valve with cover missing between the vessels can't quite work out where it is going to or coming from below, as pipe disappears behind blue vessel so I can't make comment. I would say you need to get a replacement two port to replace the motorised valve beneath the blue vessel that controls yr hot water temperature. Plus strongly recommend a service for the cylinder and all the components.
One other observation unvented cylinders also have a pressure temperature relief valve, can't make out one from the pictures. All for safety.
From what i can see from the pictures, blimey what a mess. But here goes try to make some sense of it all, mains unvented hw cylinder, that's what the blue expansion vessel is for. The other red one is for your central heating circuit. Sorry if you already know this. Under UK G3 rules it would appear that the safety release devices are not installed as per G3 requirement, these are all for safety . You can see the cold composite vale body (large black shroud) has a pressure relief that tees into pipe running across top of cylinder meets another pressure relief valve before it discharges into tundish (Not good).
As you see on last picture there is a cylinder stat albeit not as per G3 regs this should have a electrical safety cut out which kicks in if thermostat fails, which would normally be combined with the cut out correctly called Combined cylinder thermostat and `ECO (Energy cut out). You have a standard thermostat very basic, not suitable for this system really. The valve under the blue vessel would control yr hot water temp and timings as to when to come on and off (This is likely where temperature issue lies), as for the motorised valve with cover missing between the vessels can't quite work out where it is going to or coming from below, as pipe disappears behind blue vessel so I can't make comment. I would say you need to get a replacement two port to replace the motorised valve beneath the blue vessel that controls yr hot water temperature. Plus strongly recommend a service for the cylinder and all the components.
One other observation unvented cylinders also have a pressure temperature relief valve, can't make out one from the pictures. All for safety.