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Hello,
I have a non-combiboiler (Vaillant), non-condensing, non-vented with an integratedexpansion tank, that is used to heat radiators in my house. It ismaybe 10 years old and I am hoping to get a few more years from it.All of my water is heated with electrical point-of-use heaters, whichis expensive. I would like to also use my boiler for hot water byadding a cylinder and zones to my existing system. I have read a biton the forum about the S and Y plans. I have my boiler set to 70C,but in my house the boiler temperature rarely rises above 40C, unlessthe boiler has been off for a long time, and the house is very cold.In order to prevent the growth of bacteria, I would like the cylindertarget temperature to be 55 or 60C. It seems the hot water requires amuch higher boiler operating (return) temperature than the radiators.
From what I have read there are a few possibilities:
S-Plan: When onlythe cylinder calls for heat, all is fine, the boiler can go to 60C+.If only radiators call for heat, everything is also fine. If bothcall for heat, both zones will be open and heat will be taken fromthe cylinder (assuming it is up to temperature) to heat the rads.Maybe this is not a problem? In any case some kind of bypass isrequired since the Vaillant pump runs for quite some time after theflame stops, and both zones will be closed.
Y-Plan: This wouldseem ideal if there were no middle position, in middle position youhave the same issue as with S-Plan, in that heat can be taken fromthe cylinder to the rads. Maybe it is possible to find a valve withno middle position? I also have read on the forum that some kind ofextra valve is required for an unvented cylinder for Y-plan but Idon't really understand why.
Which brings me tomy question. If one makes the assumption that the cylindertemperature will always be hotter than the radiators, why not let thecylinder run wild (always open) and use only one 2-port zone valvefor the radiators. In this configuration no bypass is needed sincethe cylinder loop is always open.
Am I missingsomething?
I have a non-combiboiler (Vaillant), non-condensing, non-vented with an integratedexpansion tank, that is used to heat radiators in my house. It ismaybe 10 years old and I am hoping to get a few more years from it.All of my water is heated with electrical point-of-use heaters, whichis expensive. I would like to also use my boiler for hot water byadding a cylinder and zones to my existing system. I have read a biton the forum about the S and Y plans. I have my boiler set to 70C,but in my house the boiler temperature rarely rises above 40C, unlessthe boiler has been off for a long time, and the house is very cold.In order to prevent the growth of bacteria, I would like the cylindertarget temperature to be 55 or 60C. It seems the hot water requires amuch higher boiler operating (return) temperature than the radiators.
From what I have read there are a few possibilities:
S-Plan: When onlythe cylinder calls for heat, all is fine, the boiler can go to 60C+.If only radiators call for heat, everything is also fine. If bothcall for heat, both zones will be open and heat will be taken fromthe cylinder (assuming it is up to temperature) to heat the rads.Maybe this is not a problem? In any case some kind of bypass isrequired since the Vaillant pump runs for quite some time after theflame stops, and both zones will be closed.
Y-Plan: This wouldseem ideal if there were no middle position, in middle position youhave the same issue as with S-Plan, in that heat can be taken fromthe cylinder to the rads. Maybe it is possible to find a valve withno middle position? I also have read on the forum that some kind ofextra valve is required for an unvented cylinder for Y-plan but Idon't really understand why.
Which brings me tomy question. If one makes the assumption that the cylindertemperature will always be hotter than the radiators, why not let thecylinder run wild (always open) and use only one 2-port zone valvefor the radiators. In this configuration no bypass is needed sincethe cylinder loop is always open.
Am I missingsomething?
