Any plumbing experts awake yet?

  onthelimit1 09:16 23 Jun 2013

16 yr old house. Bathroom at rear of building has a sewer vent sticking out of the roof above the WC (soil pipes are enclosed within the building). Main bedroom ensuite on the other side of the house has no visible vent for the soil pipe. Not worried about that, but we have recently been getting unpleasant smells in the ensuite. Sniffing the shower and sink drain holes reveal nothing amiss - similar with the WC pan.

So, I assume there must be a vent somewhere to allow water to flow down the drain system. Is there such a thing as an internal vent that fits on the top of the drain that has some sort of flap valve to prevent smells which may have stuck open?

  Forum Editor 09:31 23 Jun 2013

"Is there such a thing as an internal vent that fits on the top of the drain that has some sort of flap valve to prevent smells which may have stuck open?"

Yes, there is, it's called an Air Admittance Valve (commonly a Durgo valve), and it is designed to prevent water being sucked from the traps of wash-basins, shower trays, etc. when a toilet is flushed. The flushing action dumps a charge of water into the soil pipe, and this can create a vacuum effect on smaller pipes that discharge into it.

Over a period of time it's possible that the AAV can fail, and allow soil-pipe smells to escape. It's not a problem when these valves are fitted externally, as they sometimes are when lofts are converted, but if the valve is inside the building it can give rise to the smells you're getting.

Something to check first - if you have a room that isn't used very often, and there's a wash-basin or shower in it the water in the traps can evaporate enough to break the trap seal, and this allows soil-pipe smells to escape. Shallow-seal shower traps are particularly prone to this.

  Chronos the 2nd 09:32 23 Jun 2013

Not a plumbing expert but found this. Go to the bottom,almost.

  bumpkin 10:25 23 Jun 2013

FE's last paragraph would be the first thing to check also the seal between the WC pan and soil pipe. If not that you need to locate the AAV which SHOULD be above the flood level of the basin. Check the loft area to start with. Against the regs but I have seen them fitted behind the bath panel. Sometimes they are reduced to a small 2 inch size. Usually grey or white to give you some idea of what to look for.

  onthelimit1 10:34 23 Jun 2013

Thanks all. Ladder and torch at the ready - I'll go into the loft to see what I can find.

  Forum Editor 10:38 23 Jun 2013

The valve is easy to dismantle and clean. Lofts are dusty places, and dust is the usual cause of an AAV failure.

If the valve is in the loft and has failed you'll know as soon as you go up there!

  onthelimit1 11:07 23 Jun 2013

Hmm - no smell up there FE, and no sign of a pipe, so suspect it's behind the plywood 'box' in the corner of the ensuite. Needs a bit of work to remove one of the panels, so will leave it until tomorrow (with the window left open!).

  john bunyan 12:41 23 Jun 2013

Forum Editor

I have noticed, with thanks, that you are very knowledgeable in building and other house maintenance issues - is there no limit to your talents?? Years ago I used to read the DIY magazine, but it seems to have disappeared? Was it Link Publications? I have a valve of the type mentioned and your input is much appreciated.

  woodchip 16:14 23 Jun 2013

Could the smell be coming in from top of stack pipe via wind under slats or open window

  wiz-king 16:27 23 Jun 2013

this is what to look for

  Forum Editor 16:58 23 Jun 2013

john bunyan

As some other forum members are aware, I have worked with clients in the construction industry for many years. Part of that work involves information sharing, and without going into detail, I read an awful lot of stuff about buildings and what makes them tick.

Air Admittance valves are commonplace in newer buildings, although lots of people have no idea they're there. They generally operate automatically for many years without trouble. There are occasions when a valve needs to be fitted externally. Most often this occurs when a loft conversion is built, and the occupier doesn't want an unsightly soil pipe vent rising up the side of the dormer. When the need arises there's a special, frost-proof version of the valve that's made specifically for external use. The normal type must never be sited externally.

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