Warm water from cold taps

Hi people.
I have an interesting problem with my plumbing.I shifted into a new 2 storey place a couple of months ago and have noticed of late that the cold taps are producing warm water.This only seems to occur in the mornings and is definitely heated water, not just from the warmer days.
I've googled and it appears that the problem could be from a faulty mixer that is not operating correctly.The only mixers I have are in 2 showers and one laundary tub.
Alturnatively hot water could be going back out the wrong way from the cylinder and getting into the cold supply!
It would appear an outside cold tap may trigger the problem as I notice the warm water when I water vege garden first thing in the morning.If I run the outside tap in the evenings it is cold.
Does anyone have any ideas!I think I am on medium pressure, hot water cylinder has an overflow that goes out the side of the house, with a pressure thing on it.
I'm wondering if the hot water pressure has built up so much in the morning by heating over night that it is forcing its way back through the cold inlet!
Any advice would be greatly appreciated.Let me know further info that may help work out the problem.
Cheers
Karl

Hi, give this post a bump after 6pm, when plumbers are home.

Itis more likely to be that the pipes in the ceiling are warm

Same thing happens here and as carter19 has said the pipes are in the ceiling are warm. Heat rises.

Could be a blocked aerator (Thing on the end of taps) making the hot pressure over pressurise the cold and back feeding through.
Otherwise it might pay to look at lagging your pipes in the ceiling. May pay to run the tap for 5 minutes and see if the water goes cold after a period of time or stays hot.

Wouldn't think they have plumbed in a hose tap into hot water.

It's very hot lately so are you sure it's not just that! Try running the taps for a while and see if the water gets cooler. If not, I guess it's a plumbing problem.

Hi guys.
Thanks for the replies.
I am 100% confident that the warm water is not from natural heating. I have left the cold taps on when producing warm water for quite some time and it doesn't get any cooler.The fact that the warm water only occurs first thing in the morning, and not in the heat of the afternoon also confirms this.
There is contamination from the hot water supply into the cold system somewhere/somehow, just have to figure out how.
Plumbers out there, you must have some ideas or suggestions!
Cheers

No. Any excess hot water goes out the overflow.
Otherwise your cylinder would blow up.

You outside tap is giving you a clue - it's the sun. Hot days.

I have the same "problem", and I've put it down to the sun heating the pavement the pipes run under and warming it, then releasing heat later, including into the water. Water sits in the pipes overnight, so is bound to be reasonably warm by morning. not to mention that it probably FEELS even warmer, because of the difference between water and air temperature.

Yep same here two storey house warm cold water in the summer especially this year with our great summer, soon be back too cold again when the sun disappears.