How to avoid a dead leg

Discussion in 'Plumbing and Central Heating' started by boris27, 5 Feb 2021.

  1. boris27


    25 Feb 2008
    Thanks Received:
    United Kingdom
    Hi - I have a vented, indirect hot water supply to my bathroom taps ie hot water cylinder on the ground floor, cold supply to the cylinder from tank in loft, and taps on 1st floor. The flow is ok, but could be so much better with a pump fitted - from a feed off the side of the cylinder.

    However, the feed to the taps is currently off the vent pipe to the loft. I had planned to cap off the vent, install a new vent pipe, and simply add a pump to the pipe to the taps. Installing a new vent pipe is easy as I have access straight up from the cylinder. Unfortunately, I can't cap off the old vent pipe anywhere near short enough to meet the requirements to prevent legionella as the t where the feed splits between taps and vent is completely inaccessible.

    I can access the old vent pipe at floor level in the loft ie about 2m above the t. So, my question is whether it's acceptable/workable to run a pipe from the top of the old vent and connect it back into the feed to the taps, producing a loop in that section of pipe work (after the pump) ie feed from cylinder goes to pump, feed from pump goes off and gets split into two - one going through existing pipe to taps, and the other going up the old vent pipe, and down a new pipe joining back onto the feed to the taps. What I can't find out is whether this would provide enough flow through all the pipes to prevent legionella. My alternatives seem to be just leaving it as it is, or possibly some kind of automated valve at the top of the old vent that allows a flow of water to run off each week (not looked into that one yet). Any advice much appreciated.
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    United Kingdom

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