I noticed tonight that my water heater appears to be trying to fill with cold water, but it won't stop. I can hear water flowing through the pipe, and the overflow drain pipe (white one just above the green valve) has a slow, but steady stream of water coming out. Is this normal? I've never noticed this before.

Click for full size

Suspect, water heater piping and valve

  • Depending on if the bleeder is a automatic blowout or a manual bleeder it may be the valve has failed how is the tube connected to the valve?
    – UNECS
    Commented Apr 26, 2012 at 6:53
  • Is it me or are those really sharp bends in the flexible supply line? Could that be reducing flow and causing the water through the overflow?
    – Steven
    Commented Apr 26, 2012 at 13:25

1 Answer 1


If water is flowing in the white tube, that's coming from the "Thermal Expansion Control Valve" built into the shutoff. Worst case, this could be because the thermostat or gas control valve has failed on the heater, causing the tank to get too hot.
Is the water too hot? Is there a Temperature and Pressure relief valve on the tank and is it also tripping?

If the water heater is running too hot, fix whatever is causing that. But that Thermal Expansion Control Valve (green handle) may have just failed, either way, it will probably have to be replaced.

Also, it looks like there might be a check valve (back-flow prevention) in that stack. And/or there may be a check valve on your water supply. Either way, this can cause unacceptable pressures to build up, tripping the expansion control valve and wasting water and energy.

To solve that issue, install a Water Heater Expansion Tank to keep the system at a safe pressure without tripping any relief valves.

  • Turns out the valve had failed, so this morning I ended up installing an expansion tank. Commented Apr 26, 2012 at 20:40
  • Good to hear; glad you got it fixed. Commented Apr 26, 2012 at 22:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.