Hot and Cold water seem to be mixing

Question

Having a problem with hot and cold water seemingly mixing in my house where some locations can't get cold water and others get a mix of warm/cold from hot settings.

The scenario

Moved into a new house. Has a brand new water heater and probably not new water circulation system. It appears the water heater (and probably the circulation system?) were re-plumbed for code reasons relocated from the corner of the garage next to the house along that same wall to a more central location along the wall.

Here is what I have observed

If the water circulation system is off then there is no hot water what so ever in the house.

If the water circulation unit is on then a whole range of bizarre things happen.

The kitchen sink closest to the water heater will have cold water mixed with hot (which equals pretty damn hot) coming from the cold and scolding hot coming from the hot water.

Showers (other side of the house) have alternating warm / cold water. Occasionally they can get fairly hot but only for brief (20-30 seconds) at a time. A luke warm shower (alternating with cold) with the boiler set to maximum is the best possible scenario at the moment with the current configuration.

A deep sink faucet in the garage that is directly tapping the hot/cold lines next to the water heater gets hot and cold water as expected.

Some sinks in the middle of the house get a perfect mix of hot/warm water from the hot and cold from the cold.

External water faucets/hoses on the far side and close side of the house (from the water circulation unit/water heater) pump out water that is very warm or sometimes hot.

What are some of the possible problems it could be?

Answer 1

From your comment "re-plumbed for code reasons" and the odd behavior you're experiencing, I suspect the hot water circulation system might have been patched/crossed into the cold water system and/or the pump is faulty.

For a hot water circulation to work, the hot water pipes must be in a closed system (other than the obvious exit points like a faucet, dish or clothes water connection). The pump will draw hot water from the tank and circulated it back into the tank, for as long as the pump is running. You'll always have hot water on demand.

The pump is usually a passive device, meaning if the pump is off, water can freely move in and out of the pump without obstruction. But if you're not getting hot water when the pump is off, the pump maybe faulty.

And you want to check to see if any hot water pipes got crossed/connected into cold water pipes. I suspect they are.

Answer 2

If you have a pump like this.

Then they connect the hot to the cold at the end of the lines to create a recirculation circuit so you have hot water at the sink without running the water for 5 minutes.

Some people have complained that they get lukewarm water on the cold line if the valve is not operating properly. This part here.

You may have to replace the recirculation valve or the pump or both.

Answer 3

If the hot water lines are too close or touching ,they will heat the Cold Water Line ...just Add tankless Water Heaters Where Needed, Just Cap The Hot Water Feed At The Sink Or Shower And Tee In The Tankless Heater, Only Pain Is Running The Power Lines To The Heater, Still Cheaper Than A Recirculating Hot Water System.