I have just read how to Manually flush a heating system with mains water in the ref section, & this seems fine for combi boilers but is it possible to flush a system with mains water if it is gravity fed & has f&E setup. I'm getting confused. 
Manually flush a heating system with mains water
- Thread starter NPD
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It is possible to mains flush an open system, but certain modifications have to be carried out, notably the feed & expansion (F&E) tank and open vent have to be isolated.
This is usually done by disconnecting the feed pipe and temporarily joining this to the vent pipe, with the addition of an isolating valve. The valve is closed when flushing through other circuits, but opened to allow flushing through the feed and vent pipes. But do not attempt to run the boiler with this cross connection in place.
Apart from this, more care needs to be taken when introducing high mains pressure since the system will previously only have been subject to very low pressures (determined by the height of the feed tank above the system).
It is more likely that the high mains pressure will "find" potential leaks, or even cause the catastrophic failure of a rad if the rad was so badly corroded internally that it simply couldn't withstand the pressure. The result could be a lot of nasty sludgy water spraying everywhere!
Now that I've written this advice, I have added it (with additions) to the sticky reference post on mains flushing. Any feedback on the adequacy of this guidance would be appreciated.
This is usually done by disconnecting the feed pipe and temporarily joining this to the vent pipe, with the addition of an isolating valve. The valve is closed when flushing through other circuits, but opened to allow flushing through the feed and vent pipes. But do not attempt to run the boiler with this cross connection in place.
Apart from this, more care needs to be taken when introducing high mains pressure since the system will previously only have been subject to very low pressures (determined by the height of the feed tank above the system).
It is more likely that the high mains pressure will "find" potential leaks, or even cause the catastrophic failure of a rad if the rad was so badly corroded internally that it simply couldn't withstand the pressure. The result could be a lot of nasty sludgy water spraying everywhere!
Now that I've written this advice, I have added it (with additions) to the sticky reference post on mains flushing. Any feedback on the adequacy of this guidance would be appreciated.
With vented systems, it is necessary to cap off, or loop together the F&E pipes.
The F&E pipes may be capped with push fit end caps, such as Speedfit or Hep2O, or a temporary compression fitting gate valve.
Looping the feed and expansion pipes together will enable these pipes to be flushed during the cleansing process, which can be beneficial when the cold feed pipe contains corrosion deposits.
This will only be effective when the F&E pipes are not close coupled, or connected via an air separator, and will not remove deposits which have hardened over a long period of time.
If an antigravity / check valve is present, this must be by-passed or bridged to allow the flow reversing action to be used. It may be possible to dissemble the antigravity valve, and remove internal components.
The F&E pipes may be capped with push fit end caps, such as Speedfit or Hep2O, or a temporary compression fitting gate valve.
Looping the feed and expansion pipes together will enable these pipes to be flushed during the cleansing process, which can be beneficial when the cold feed pipe contains corrosion deposits.
This will only be effective when the F&E pipes are not close coupled, or connected via an air separator, and will not remove deposits which have hardened over a long period of time.
If an antigravity / check valve is present, this must be by-passed or bridged to allow the flow reversing action to be used. It may be possible to dissemble the antigravity valve, and remove internal components.
Gasman, good point about the anti-gravity valve, which I will add into my reference post.
But.....you refer to the F&E pipes. A common mistake, but as I'm sure you know the F&E pipe is one pipe, the other being the Vent pipe.
But.....you refer to the F&E pipes. A common mistake, but as I'm sure you know the F&E pipe is one pipe, the other being the Vent pipe.
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Yes Chris, thankyou, it is more of a layman term.
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I hooked a radiator off in the kitchen. Made myself a little 'system' so that I could put the water into either radiator valve and dump it out of the other. I used 4 valves but could have used 2 of those T (3-port) valves. Enabled me to reverse the flow.
Choose the kitchen as any spills were no problem. Otherwise as above.
Choose the kitchen as any spills were no problem. Otherwise as above.
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