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Draining and Cleaning an open vented system

Postby zuumah » Thu Jul 26, 2007 6:27 pm


I need to try and clean my pipes and radiators internally, I wondered could i put a hosepipe on an outlet on a radiator and let the water run out until it was cleaner?
In other words dont tie up the ballcock in the expansion tank so that there is a constant flow of water through the system.... I cant afford to mechanically flush it..
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Simply Build It

Postby wingleburtbenglebink » Fri Jul 27, 2007 12:48 pm

You could but it will not have much effect. How about connecting your outside tap if you have one to a hose and firing mains water into the system via a drain cock. It is crude but will give more benefit than gravity. Also you will be backfilling the header tank so you will need to take care not to cause overflow. It may be worth draining the system and cleaning the header before commencing. Periodically you will need to stop the hose, disconnect from the tap and let the water drain back out. You can control which rads are being flushed by isolating them on the valves. The system should have been balanced so make a note of how many turns open each valve is and restore the valve to the same position when you finish. You risk moving sludge around and blocking parts of the system or worse creating leaks from marginal joints, but if you need a flush and cant afford it you dont have a huge array of options. I have used this method successfully on badly sludged legs of systems. You may need to stop end the vent pipe that is over the top of the header tank and you need to jubilee clip the hose pipe to the drain cock. Finally if your tap does not have backflow prevention you will be violating water bylaws and could introduce central heating water into the mains supply that is distributed to the neighbourhood - bad form. Have fun.
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Postby johnb » Wed Aug 01, 2007 7:43 pm

hi zuumah why do you need to clean system john
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Postby htg engineer » Thu Aug 02, 2007 3:16 pm

wingleburtbenglebink - Just remember this is not a pressurised system, so applying mains cold water pressure could cause leaks on pipework, radiators, tanks and boiler.

Heating systems which are power flushed are forcibly cleansed using water at high velocity, but low pressure, so that no physical damage is caused to the system.

So not a good idea to apply mains cold water pressure.

You could use a hose pipe, but keep pressure low and allow to run till clear. Add descaler or cleanser which can be bought at any diy store or heating / plumbers merchants. Allow system to run for a couple of days and drain again, flush and add inhibitor.

And as johnb asks whats the reason for wanting to clean system ?
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Postby muzza » Thu Aug 02, 2007 7:19 pm

Adding a cleanser/flushing agent to the header tank is a better idea, leave it in as per instructions then drain and refill.

But unless you have serious blockages, leave it alone, draining and refilling introduces oxygen and encourages corrosion. After a short period in use the water in your system becomes pretty much de-aereated so leave it alone unless you have serious prblems
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