Engine heating water to ALL faucets (hot and cold)

[pma_foyl]

When running the engine for an extended time, it is heating the hot water heater (as it should), BUT it is now somehow providing hot water to ALLfaucets. No cold water is available.

Had this problem before and thought the check valve (on the manifold) was to blame. I swapped it out and seemed to resolve the problem. But now it’s happening again and I have no idea what could be causing it.

Any ideas would be appreciated.

[stevead]

Climate change ?

[Bill O]

Not sure which manifold you are talking about with a check valve, but most of the time I've seen the check valve on the cold water supply as it goes into the water heater tank.
How long ago did you change the check valve? (possibility it needs to be replaced again)

[pma_foyl]

Thanks Bill,
That’s the check valve I JUST replaced (on the input of the water heater). Less than 3 months ago.

[wholybee]

Two things I can think of. Do you have a mixing valve that might have failed? Also, there should be an expansion tank between the check valve and hot water tank. Many installations don't have it, (mine doesn't) but the problem you have is what it is for. See these installation instructions for a Raritan tank:
https://manuals.plus/raritan/raritan...anual#plumbing

[Bowdrie]

This may seem overly simplistic, but water would much rather flow in a straight line than thru tight 90 fittings.
The main cold-water supply probably reaches a T fitting, thence it has 2 ways to travel, one to the cold-water faucet(s), one to the inlet of the heater.
If so, have the "branch" side of the T feed the heater, the "run" of the T being the continuance of the cold-water flow to the fixtures.
Those check valves are miserable devices, the "swinging gate" style need to be mounted vertically so that gravity will help them close, (and they're still wretched).
After having replaced a couple on my own system I just eliminated the check valve entirely, any heat that migrates back into the cold-water inlet is quickly defused/dissipated and no hot, (or even warm/tepid,) water reaches a cold faucet.
Since I'm now on the boat, (water heater has been on for hours,) I just checked the cold-water inlet, and ~10>12 in. back up the inlet hose the water is cold.

[ItDepends]

Also, do not forget the obvious...

There are water hoses in the engine room...
When the engine is running the engine room gets hot...
Therefore the water in the hoses in the engine room gets hot.
Even the "cold water" hoses.

[Bill O]

Originally Posted by pma_foyl

Thanks Bill,
That’s the check valve I JUST replaced (on the input of the water heater). Less than 3 months ago.

Was it a one way brass ball or gate valve? Is there debris (anode) in the tank causing the valve to not close?
Again if it worked initially, did anything unusual happen that could have caused it to fail?

[rslifkin]

Originally Posted by ItDepends

Also, do not forget the obvious...

There are water hoses in the engine room...
When the engine is running the engine room gets hot...
Therefore the water in the hoses in the engine room gets hot.
Even the "cold water" hoses.

Exactly this. My boat has a bunch of plumbing in the engine room, so if things are running and warm for a while, the first bit of cold water you use will come out warm (not as warm as the hot water though).

[MWGDVC]

Failing tempering valve?

[Bent Bugle]

Could only be a failed tempering or check valve, if replacing the check valve resolved the issue for a while there's your answer...install a good quality spring loaded valve...it sounds a bit strange, even with no valve you should get cold water coming thru after a little while...

[Chotu]

I’m thinking the Coldwater plumbing going through the engine room also. That was my first thought. Especially if you know the check valve is good. You do know this? It’s definitely good?

[Lepke]

In a small system there should be a small expansion tank on the hot side. As the water heater rises in temp the water expands. If no faucets are used it has to go somewhere so it backs up to where cold is teed off to the heater. Many check valves slowly leak at constant higher pressure so the hot water slowly fills the cold line towards the tank, pushing the cold water before it. Even thru some pumps. Now to get cold water, all that hot in the cold line has to be used first.

I use a bronze check valve with a flapper. but no spring. It's installed so the flapper is near horizontal and closed at rest.
Depending on where the engine water is pulled from it may be supplying more heat when running at high rpm. Causing more water expansion.

[Rumrace]

The cold water should be coming from your tank while your hot water coming from a water heater tank an insulated accumulator. The water heater by the engine came from the tank so the splice is on the wrong end. What every you changed last ….