What is pumping over?
Pumping over occurs when water is pumped over the open vent pipe and into the feed and expansion header tank. This cannot happen in sealed systems. It can be caused by an incorrectly placed circulator, too high circulator speed, insufficient static head or incorrectly sited system components. Conversely, seesawing is where water is pumped up the feed and expansion pipe. In either case, if there is enough thermal contraction then re-oxygenated water will be drawn into the primary circuit which will promote corrosion. The first likely evidence will be pinholes in radiators. A correctly installed system will create positive pressure in as much of the installation as possible. The diagram below shows correct ‘left to right’ and ‘right to left’ installations. If the order in your system is different then we recommend you contact a qualified plumber.
