Why is it necessary?
The reason for this is that modern high efficiency boilers have much smaller heat exchangers; and are prone to blockage: especially the plate heat exchangers on combination boilers, which can act as a filter, become blocked and effect the production of domestic hot water**.
On older heating systems, especially those that once incorporated a “feed & expansion tank” then sludge will be present as well as other contaminants such as “flux”. It may be that the boiler being replaced is a combination boiler at the end of its serviceable / working life, and that; it replaced a boiler that had its primary (water) circuit vented to atmosphere. During this previous time of replacement a proper flush may not have been performed!
It has been stated that 75% of boiler manufacturer call backs are associated to contamination / debris as the cause. Not having a heating system properly flushed may affect the boiler manufacturer’s warranty.
Where possible it may be useful to use the existing boiler to assist in performing the flush. Though power flushing units may incorporate a heating unit; the time factor involved, to heat the system could be reduced and the procedure different. We only use trusted equipment from Fernox.
The duration of work will vary, being dependent on the individual circumstance of installation.
If a radiator develops a leak anywhere, other than at a connection; it is a good indication of corrosion within the whole installation: an inspection at the “feed & expansion tank” can provide a good indication of the internal condition, especially if honest & accurate installation / service history is available. If replacing a radiator due to leakage / pin-holing; close inspection of the failed radiator may be a useful indication to the general condition of the heating system!
Whilst power flushing will enhance the efficiency of an old dirty heating system: The pressure developed by the machine is more than that developed by the average domestic circulator (pump); but not more excessive than the pressure of which a properly installed and sound system, should be capable of handling!
It is fact that if an “open vented” boiler is replaced by one of a “sealed system” (mains pressurized); then a greater internal system pressure will be developed during operation. This could be a consideration, when selecting a replacement boiler. (Vaillant produce an open-vented condensing boiler) Parts of a system that have failed due to severe corrosion may become apparent, during the power flushing procedure. Control valves may be used during the process of a power flush, that haven’t been operated for many years. They may start to leak if used. If this happens during a power flush: though not at fault, the engineer would endeavor to assist the home owner, to resolve the problem.
I have been called to properties where several plumbers have recommended a power flush; and it was not the case!
A good level of knowledge in “plumbing & heating” will assist in a successful power flush: reducing the likely hood of problems occurring, and being able to deal with them should they occur.
Not referring to lime scale blockage due to hard water! It is advised that that all combination boilers installed within hard water areas are protected by a Combimate or similar water conditioner!