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4) Fill Valve (Required) – Either a manual or automatic ll valve may be used. The ideal location
for the ll is at the expansion tank.
5) Automatic Air Vent (Required) – At least one automatic air vent is required. Manual vents will
usually be required in other parts of the system to remove air during initial ll.
6) Low Water Cut-Off (Required in some situations) – A low water cut-off is required when the
boiler is installed above radiation. In addition, some codes such as ASME CSD-1 require
low water cut-offs. Codes may also require that this low water cut-off have a manual reset
function. The low water cut-off may be a oat type or probe type but must be designed for use
in a hot-water system. The low water cut-off should be piped into the boiler supply just above the
boiler with no intervening valve between it and the boiler.
Use a low water cut-off that breaks the line voltage electrical supply to the boiler.
7) Manual Reset High Limit (Required by some codes) – This control is required by ASME CSD-1
and some other codes. Install the high limit in the boiler supply piping just beyond the boiler
with no intervening valves. Set manual reset high limit as far above the operating limit setting
as possible, but not over 240F. Wire the control to break the line voltage electrical supply to the
boiler.
8) Flow control valve (Required under some conditions) – The ow control valve prevents ow
through the system unless the circulator is operating. A ow control valve may be necessary
on converted gravity systems to prevent gravity circulation. Flow control valves are also used to
prevent “ghost ows” in circulator zone systems through zones that are not calling for heat.
9) Isolation Valves (Optional) – Isolation valves are useful if the boiler must be drained, as they will
eliminate having to drain and rell the entire system.