DIY Heating Plumbing Tips 4 - Power flushing hydronic (water-based) central heating systems is basically the flushing of the 'heating circuit's' pipework, heat emitters and boiler heat exchanger with high velocity low pressure water.
When a hydronic central heating system is newly installed the system should be power flushed to remove any installation debris such as; pipe solder, wire wool or other foreign matter. This debris can interfere with the opening and closing of the system valves and later contribute or cause corrosion within the central heating system.
When you upgrade your central heating system, e.g, with a new boiler, the primary circuit (the heating pipework) and heat emitters (radiators) should be power flushed to remove any sludge, and chemically treated to prevent any future corrosion, sludge or limescale build-up occurring within the system.
Sludge and limescale build-up will reduce the performance of your system by between 5 and 15%.
On this page you will find sections on:
Power flushing is the use of a powerful self contained flushing unit designed for cleaning hydronic (water-based) central heating systems with the aid of chemicals.
There are a number of power flushing units now on the market and they generally do the same thing - they are designed to circulate high velocity water around the heating system. These power flushing units offer reverse flow circulation, water dumping to remove sludge, limescale and dirty water, water replacement and chemical treatment.
When air gets into a hydronic central heating system - corrosion will take place:
Limescale build-up can seriously damage your boiler's heat exchanger by insulating the heat exchanger and causing localized boiling, reduced heat output and boiler failure.
Click the thumbnail below to to view the spots of accumulated sludge in a central heating system - opens in new window.
A power flushing unit may be connected to the hydronic central heating system by:
Some power flushing unit manufacturers supply pump adaptors that connect directly onto the pump by removal of the pump's 'plate', this eliminates the complete removal of the pump to connect the flushing unit.
If you can't get access the central heating pump then you can connect the power flushing unit via the valves on the radiators tails (flow and return pipe) by first closing off the radiator valves, (user control valve and lock-shield valve) and then detach the valves from the radiator and drain.
To close off the lock-shield valve remove valve cap then untighten the top lock-nut then close off the valve spindle by turning clockwise with a flat head screwdriver.
Once the radiator has been drained and removed the power flusher's flushing hoses can then be connected to the flow and return valves on the radiator's tail pipes.
If connecting to copper or steel tail pipes then you need to be sure that the supplementary bonding the 'earth continuity bond' is maintained by attaching a temporary earth bonding wire to the tail pipes before detaching the radiator
Note: If you have an open-vented system then you will have to isolate the 'feed & expansion cistern/tank' main service valve, or tie off the ball (float) valve, and cap off the open safety vent pipe before you connect the flushing unit. The water in the 'feed & expansion cistern/tank' can then be drained into the reservoir of the flushing unit.
Note: If you have a sealed system then you will need to first drain down your system until it is no longer pressurized before you connect the flushing unit
To prepare your hydronic central heating system for power flushing you should:
Generally power flushing units are connected to the hydronic central heating circuit via the circulator pump's unions after the pump has been removed.
Some manufacturers provide pump 'adaptors' that connects directly onto the circulator pump. This device eliminates the removal of the pump to enable the connection of the power flushing unit.
The power flushing unit can be connected to the heating circuit by draining the boiler and disconnecting the boiler's primary flow and return pipes. The unit can then be connected to the primary flow and return whilst the boiler is disconnected
The power flushing unit can also be connect via the radiator tails (flow and return pipes). If you connect via the radiator tails, then be sure to remember to flush the individual radiator you have disconnected after you have completed flushing the heating system.
Once the power flushing unit has been connected to the heating circuit and the water inlet hose is attached to the unit, make sure that both the dumping & overflow hoses terminate at a suitable drain.
If your heating system is open vented, then once you have isolated the water supply to the 'feed & expansion cistern/tank' by closing the service valve or by tying off the ball (float) valve you can drain the water from the 'feed & expansion cistern/tank into the power flushing unit.
Along with the water in the heating circuit, a minimum level of water must be maintained within the unit's reservoir to enable the flushing operation.
Power flushing procedure:
When completed, the power flushing unit can be isolated and disconnect from the heating circuit and the heating system can then be reinstated for normal operation.
To power flush a system with ten radiators, will take roughly 4 to 8 hours depending on the severity of system scaling and rust.
Be aware, that when using descaling chemicals in older hydronic central heating systems with many years of corrosion, there is the possibility of leaks occurring from pin holes in the radiators once the corrosion and sludge has been treated and removed.
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