Hot water on the cold side

[reicherb]

Starting recently, when I run the cold water, I get surges of hot water through the cold lines. It seems to only happy when the pump is not running. When the pump kicks in, the water goes cold again. when the pump turns off, I get surges of hot again.

My guess was that the check valve on the hot water tank has gone bad. Upon quick inspection that appears not to be the case. I can't blow air through it either way. Maybe the valve is beginning to fail?

Maybe it's something with the pump causing water not to flow through when it's not running?

What is the most lively culprit?

Thanks,

Brad

[DrewE]

Since you don't have an accumulator tank, you should not really have water running without the pump (assuming you aren't connected to city water). There might be a really quick spurt from the pressure in the piping, which is slightly elastic, and the small air space in the water heater, but not a more continual flow. If you're hooked up to city water, there's generally no reason to have the water pump on at all.

Anyhow, the only way you generally can get hot water in the cold lines is if the bypass valve is not set properly (i.e. open) or there's a shower with the hand knobs on and the valve at the spray head shut off, which amounts to the same thing. While more commonly it's the outside shower that gets overlooked and not shut off fully (because of how it's often used to rinse stuff off and because it's more out of sight), the inside ones will also behave exactly the same way.

[reicherb]

I don't have an accumulator tank or outside shower.

I have a 3 valve system.

The check valve on the water heater checks good. Using my air compressor, I can only blow air in one direction.

Brad

[DrewE]

Old-Biscuit wrote:

Do you have an accumulator tank?
W/O one no water could flow without pump on (or city water hooked up)

If you don't have an accumulator tank and you still get more than a half-second of flow when the pump is off, it's possible to have the water heater act as an accumulator tank in some cases if the winterize valves are set incorrectly. In particular, if it's a three-valve setup, having the cold valve open, the bypass valve open, and the hot valve closed will make it a very nice six-gallon pressure tank and let hot and cold water mix more or less arbitrarily. (If you have a three-valve winterization setup, you probably don't have any check valves associated with the water heater.)

Please don't ask how I know this is more than just mere theory.

[Old-Biscuit]

corvettekent wrote:
Check your outside shower and make sure that both the hot and cold faucets are turned off.

X2

Only 2 places that hot/cold can mix together
Shower fixtures when NOT turned off via hot/cold knobs (just button on handle) Could be inside or outside shower
AND
Water heater bypass valve....closed for normal (Open when winterizing)


Check valve in WH Tank Hot outlet (top fitting) is a cheap plastic plunger/spring/o-ring assembly.
They can plug/clog....no hot water flow
The o-ring can get dislodged/go bad.....then they allow back-flow into WH Tank
They can jam.....no hot water flow

Do you have an accumulator tank?
W/O one no water could flow without pump on (or city water hooked up)

[corvettekent]

Check your outside shower and make sure that both the hot and cold faucets are turned off.

[agesilaus]

If the check valve has a spring in it, that could be getting weak.