Warm water from cold taps unvented cylinder

The best way to test, is as advised. Shut down all the heating for 24hrs and then run the tap, if it's cooler/cold than normal then that's your issue and it will be thermal transfer and then it's time to trace the pipework.

I really wouldn't suspect it's expansion as 30secs worth is a fair length of pipe to be contaminated, that and there's a new combi valve so the check valve should be working fine.
 
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It's difficult to do as we may obviously use a toilet, tap, dishwasher etc

Now you get an idea of what it's like being a plumber!
Most annoying thing for me is the question "have you turned the water off?"
My stock answer is "no, that'll be the electrician"...
Answered with: "but there's no electrician here!" :rolleyes:
 
Hi, thanks again for your input and as one last effort niwi have tried the suggestions, I turned the CH and UFH off so only hot water on and there was definitely improvement but the cold water still didn't get warm for at least 20secs.

When I then turned the UFH on and that was on throughout the day then the water got warmer but for approx same amount of time. Not sure why this would be when UFH is only downstairs but it is making the boiler work for longer.

When we run the hot tap for a while the cold then seems to remain colder without going through the 20sec cycle but what I do feel is what I think is a glut of warm water going down the cold inlet pipe to the cylinder.

However, the other day I was running the tap and it was warm, then stopped it and turned back on and it was cold. Just seems to happen so randomly sometimes but then had a generally same cycle most of the time but one thing I can say is once one tap has got the warm water out then if I turn any other cold tap on then that tap remains cold.

Not sure if that gives any indication of anything else but those are my findings from a week of trialling things if you can give any ideas. Plumber says pipes all adequately spaced and think I have a couple of photos I can hopefully find and post
 
Here is one pic of pipe spacing
 

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Here are the 4 pipes that were installed. I think the 2 on the right are the cold feed in and cold balanced out.

I assume the others are hot and CH but thought I'd share so you could see spacing more than anything.

Thanks again
Phil
 

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If those pipes in pic 3 are boxed in together without any insulation and the 2 on the left are hot then that space will be getting warmed and at that point at least, so will any standing water in the cold pipework.
 

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