Regulations for Vent from immersion tank to feed expansion tank

Discussion in 'Plumbers' Talk' started by Martin Jones, Jan 22, 2017.

  1. Martin Jones

    Martin Jones New Member

    Hope someone can help please.
    I am thinking of moving the expansion tank for an immersion heater into the attic however this will require the vent pipe to go under the level of the tank before it rises up into the tank in the attic. The tank is high above the immersion heater but the track of the vent pipe would need to go downwards first. Is this possible/advisable? Are there any regulations controlling this?

    Any help would be appreciated. Thank you.
  2. Glad its Friday

    Glad its Friday Active Member

    Got to rise vertically.
    I think it has to also rise 350mm above the level of water in the f/e before bending back down into it, (would need to double check that).
  3. nigel willson

    nigel willson Screwfix Select

    Get a plumber to do it you obviously don't know how it works, you'll get all sorts of grief otherwise.
  4. Tricky Dicky

    Tricky Dicky Screwfix Select

    The vent pipe must be a minimum of 22mm diameter, insulated for at least the first metre of its run and it must run constantly upwards to it's maximum height. Otherwise it can't act as a vent pipe.
  5. Martin Jones

    Martin Jones New Member

    OK thank you. That clarifies things. Many thanks :)
  6. Dr Bodgit

    Dr Bodgit Super Member

    Well mine is only 15mm...quite a short length though so can't see any issues. I dare say the regs dictate 22mm so that is what you should use. No reason not to use 22m really as the hot water pipes will be 22mm, just that mine were run in 15mm and couldn't be ar$ed to change it.

    I don't see why it needs to run constantly upwards, if it dips for a while it won't affect its operation.

    IIRC, it should rise to 450mm above the water level before coming down "into" the tank (just above the water line, entry via top of the tank/lid).
  7. Glad its Friday

    Glad its Friday Active Member

    See quite a few 15mm pipes on old systems, work ok provided not too long, some are even combined as a feed and vent pipe.
    Has to continually rise - think about it - air going downhill.....?

    Checked the reg (I may be out of date here note). Measure the head of water from the bottom of the hot water cylinder, add 4% add on another 150mm.
    So if you've a 3m head (4%=120mm) +150mm = 270mm
  8. Dr Bodgit

    Dr Bodgit Super Member

    If the pipe goes down, the air will simply be pushed along/out/up by the pressure of the water.

    Can't think how a combined feed and vent pipe would work :confused:
  9. Pollowick

    Pollowick Screwfix Select

    Will it?

    Air locks don't always behave in a logical or expected way! For example:

    My cold tank had a hot take off which went across the attic for a couple of metres with an initial down slope and then horizontal before turning through 90 degrees and vertically down to the cylinder below. At some time, a previous owner decided to install a gate valve in the vertical run so they cut the pipe and lifted the top up inserted the valve, tightened up. One day, after draining down I could not get a decent water flow from the hot taps, we checked everything including rods through pipes to check it was clear. After refilling again we finally found an airlock at the right angle bend and it could only be shifted by either pressure on the hot system or draining most of the cold storage, then lifting a few inches ... and once cleared relocating and refilling. All because someone could not be bothered to cut out 20mm of pipe.

    If the vent pipe runs down for just a small amount, you could get the same type of problem.
  10. Dr Bodgit

    Dr Bodgit Super Member

    Yes it will, in this case, as the vent pipe cannot air lock - the end of the pipe is open. The vent pipe is different to a feed or C/H pipe in this way, as its totally open and will let water flow if there is sufficient pressure to "vent".

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