Rubber taste in cold water - unvented cylinder system

[tomyd]

Hi All,

I had an unvented, indirect water system installed in the house during a renovation about 18 months ago. About 12 months ago I started noticing a rubber taste and smell in the cold water. This was coming out of all of the taps and showers in the house and has been getting progressively worse over time.

I've investigated on the internet and forums, the closest (and about the only) post I can find about it is this one:

//www.diynot.com/forums/viewtopic.php?t=129365&start=0

It appeared to point to a query in the plumbing layout. As such I looked at the pipework and tried to figure out what went where. I'm unsure as to whether the expansion vessel and the cold water feed are plumbed in the correct place. It would be greatly appreciated if someone/some people could have a look at the pictures I've added below and let me know whether I should have any concerns.

As an aside, the smell/taste does not seem to come out of the hot water. The heating engineer was Gas Safe registered, however I wasn't aware of the G3 qualification prior to my investigations so I'm unsure as to whether he has it.

I've mentioned the problem to him and he says he's never heard of it before!

Thanks in advance for your help!

 

[tomyd]

I should add that the rubber taste is only present when running a tap for the first 20 - 30 seconds, it then seems to be washed through when the fresh water from the mains pipe comes through.

Thanks again!

 

[bolshy]

If that's your mains cold water pipe on right of picture, your expansion vessel is connected in the wrong place and in any case should have a check valve preventing any backflow, between where it connects and the incoming cold mains. I can't see one.

 

[tomyd]

Sorry for the lack of clarity, the mains water is in the right middle of the pictures, flowing from left to right near the black pressure release valve in the middle of the pictures. Hope that helps!

 

[bolshy]

In through the yellow ball valve, then the combination valve? This has a built in check valve, I believe, I thought it was a PRV at first. IMO the rubber taste would be coming from the neoprene bag in the expansion vessel, surely. Where does the vertical cold water pipework on the right of the picture go, besides to the cylinder? And where does the 15mm pipe leaving left from the T by the expansion vessel go?

 

[tomyd]

That's correct, in through the combination valve, flowing left to right.

The 22mm down pipe straight after the combination valve feeds the cylinder. The 22mm pipe on the far right goes to taps/showers upstairs and downstairs.

The 15mm to the left of the expansion vessel goes straight to a tap in the utility room (where the cylinder is located).

I'm wondering now whether the neoprene bag in the expansion vessel would give off a taste, irrespective of the plumbing? Is it this that could be faulty or is it the plumbing layout that's incorrect.

Thanks for your help so far, it really is appreciated. And if any more photos would help, just let me know.

 

[bolshy]

You shouldn't have any potable water drawn off the system after that combination valve, the check valve in it is to prevent backflow contamination of your cold mains water from the expansion vessel or your cylinder. All of your cold services should be taken off before the combination valve, ESPECIALLY drinking water. If your incoming mains pressure is high, a separate Presssure Reducing Vv can be installed to control shower cold feeds, but again teeing off upstream of the combination valve.
The expansion vessel is where the rubber taste and smell is coming from. Those cold water services need repiping to the incoming cold supply before the yellow ball valve. The only things that should be connected downstream of the combination valve are the expansion vessel and the cold feed to cylinder, and of course the pressure relief (again, this is part of the combination valve in this instance).
Clear guidance is given in the Water Regs on unvented systems.

 

[tomyd]

Thanks so much for your response. It's confirming what I'd thought.

I'll have a read of the regs to get a better understanding.

One query though, is there a requirement for a balanced cold water feed after the combination valve? I'm a bit confused as this seems to be suggested on some installation manuals.

Thanks again.

 

[bolshy]

If possible, your cold water services should be taken off before the combination valve. You may require a balanced pressure for some mixer showers, but as I said, this can be achieved using a separate pressure reducing valve, and you may not need balanced feeds at all. If you tee off cold water services after the combination valve, these should be for showers only.
arghh, gotta go I'm afraid, will be back on forum later........