Tracing eggy smell from drains or heating system

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Hi everyone. I'm looking for inspiration to try to track down a disgusting eggy smell which appears in my house from time to time.

Our house was built around 1965-1970. We moved in about 5 months ago. Straight away we noticed occasional foul eggy whiffs which came out of nowhere and disappeared again after a couple of minutes. We have been unable to find the source.

At first we suspected a drain problem but can't find anything wrong with the drains. We dug up a section of surface water drain outside and found a great big hole in the top of the pipe which we have now replaced. However the smells still happen.

Our house was extended some years ago to build over the driveway. Consequently our soil stack is part inside and part outside the house. The internal portion is boxed in. We have cut a hole in the boxing but get no smells from within. The soil stack seems fine. It connects to an underground chamber beneath the (now internal) floor and then runs off to the street. The chamber is completely covered over with tiled flooring. Before moving in we had a camera survey of the foul drain which revealed no problems.

As I can find no faults with the drain runs I am starting to wonder about central heating. This is where it gets interesting. Initially the smells were in two places - the rear lobby and the upstairs bathroom which is above the rear lobby. The boxed in soil stack is also in the rear lobby and two upstairs toilets connect to it. We had a brand new combi boiler installed a couple of months ago and since then the bathroom smells have all but disappeared. However we still get them in the rear lobby and they have started to appear in the front lobby as well. It's as if something has caused the smell to relocate.

The timing may be coincidental but it seems odd that the bathroom smell (which was VERY strong) goes away round about the same time as we get a new boiler fitted. The new boiler is in a different location from the old one so new underfloor piping has been laid and old piping is now partly redundant.

Before the new boiler was commissioned we had a power flush so there should be no foul sludge in the system. Pressure on the boiler is good with no evidence of leaks.

I'm out of ideas. Any suggestions?
 
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At first we suspected a drain problem but can't find anything wrong with the drains. We dug up a section of surface water drain outside and found a great big hole in the top of the pipe which we have now replaced. However the smells still happen.




I'm out of ideas. Any suggestions?
Venting of the drains :idea: look for the ubiquitous Durgo valve - then bin it and vent properly ;)
 
probably hidden in a boxing or roofspace . Have a google for durgo and drain venting - you`re sure to find some diagrams . Also look outside the house for a vent pipe going through the roof ;)
 
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The vent pipe going through the roof is open at the top as it should be. There is a boxed in section of pipe in the downstairs loo which could well contain a durgo valve at a lower level than the cistern. Flushing this loo doesn't cause any smell, however this waste pipe connects to the main soil stack in the back lobby where the smell is. Is it possible this valve could be the cause even if it doesn't cause any smell when that particular loo is flushed?
 
OK sounds like you have a sensible setup ;) Next check the water seal in the traps of basins, bath, shower,sink etc. .Just use a dry stick as a dipstick - make a note of the depths . Then when you get the whiff, go round and check again - see if any of the traps have been pulled , allowing the smell back :idea: Time consuming, but ideal for DIY and may well indentify the problem area .
 
The vent pipe going through the roof is open at the top as it should be. There is a boxed in section of pipe in the downstairs loo which could well contain a durgo valve at a lower level than the cistern. Flushing this loo doesn't cause any smell, however this waste pipe connects to the main soil stack in the back lobby where the smell is. Is it possible this valve could be the cause even if it doesn't cause any smell when that particular loo is flushed?
Not likely ;)
 
OK well after some further investigation it seems the traps aren't pulling. The sink in the bathroom where the smell appears has an anti-syphon trap anyway. What I have discovered, by removing a section of the ceiling below the soil pipe (which is partly internal to the house) is that a floor joist is getting wet where it is in direct contact with a section of the soil pipe. That suggests a leak in the soil pipe immediately adjacent to the joist. Condensation on wood sounds unlikely to me and it is definitely wetter when water services have been run above.

The thing that seems to trigger the smell is flushing the loo followed by running a cold water tap at the sink in the same room. Just flushing the loo doesn't make the smell come out, it's turning on the tap afterwards that is the trigger for it. However the outlet from the sink doesn't connect to the soil pipe and has an independent exit to a hopper outside so is venting to fresh air.

Assuming a leaky soil pipe is the cause, what is puzzling me is (a) why there isn't a smell all the time (b) why the smell appears in different places and (c) why it seems to be triggered by running a tap. Any ideas?
 
OK well I've found the cause. Fortunately no need for major repair work as far as I can tell. Amazing how such a horrible smell can come from such a small area.
 

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