TOPIC: Cold water, then hot water, then cold again on all cold side faucets

A friend of mine has an ongoing problem with all the cold water taps in their home.  When the cold lines sit for a while and then turned on, the cold runs for about 30 seconds.  Then the water heats to full hot for about a minute.  The water then cools to cold.  This will happen on all faucets. 

Talking to my friends on the phone (until I can get over there), the husband "apparently" confirmed to me there is no expansion tank on either water tank (they have two water tanks).  I also confirmed they have some single-lever faucets in the house.  The house is about 5000 sq feet.  I am thinking of checking the single lever faucets for cross connections from failed seals, but wondering if that would cause this problem at all faucets in the house.  Anyone ever come across this before?

I do not think cross connections would be occurring, I think you would see leaking. Are there circulating pumps installed? They may be failing. How old are the water heaters?

At this point I don't think you have enough details.  Here's some of the questions I would have for your friend:

1. Does "ongoing problem" mean it has always happened since they bought the house?  Or was there a approximate start date for the issue.
2. Are all the times you mentioned actually timed?  Tap on, then exactly 30 seconds of cold, then exactly 60 seconds of full hot?
3. Was the "full hot" a measured temp, or was it relative to the cold water he felt for the first 30 seconds?  All the times and temps sound very approximate and that in itself may be important.
4. Where is the home located?  In a cold climate where a furnace or boiler is running?

If it is in a cold climate, has he checked to see if he has water pipes running through or on top of ducts or boiler pipes?  I would look for some heat source that is transferring heat into the main cold supply line.  I have seen houses with similar setups run cold, then warm(hot may be relative), then cold again just because one of the cold lines is getting heated while the water sits.  Rule out the simple, then branch out into cross connections and all the other possibilities. 

Any chance this is a tankless water heater?

Thank you for the quick replies gentlemen.  The questions you listed are what I will be checking when I get to their house.  I will repost once I gather the data.  BTW, this apparently has been happening since they purchased the home about three years ago.  I am interested to see if a pipe manifold is hovering over a heat source since it is happening at every faucet.  Chat soon.

No.  This house has two tanks, which I will get the data from.