Help explain how this tank works (to solve a problem)

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Batman

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#196646 7-Jun-2016 19:55

Hi this tank has a drain at the top, and when I'm not using hot water, water flows out of the drain at the top of the tank. (Sorry this is how I am able to explain it). When I use hot water, the drain stops draining water for a few hours. [Note pic not of actual malfunctioning tank]

I climbed up to the roof cavity to take a look and it seems that when I use hot water for kids' bath, the level in the tank drops a 3 inches. Then when the water tank heats up the level rises until it constantly runs out the overflow drain. (I haven't re-checked to see if the "floating ball valve" is leaky however)

Why would the water rise and fall in the first place? Is my water heater thermostat broken?

Yogi02

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#1567436 7-Jun-2016 20:03

This is a hot water cylinder header tank. The volume and height is what gives you your hot water pressure.

Cold water comes in through the stop cock valve (same as in water troughs for cows) The drain is an overflow in case the stop cock doesn't stop incoming supply.

As you use hot water, water empties from the cylinder and is gravity fed from this tank, when the stopcock drops with water level, cold water starts filling header tank, when it is full, the upward pressure of stopcock should close valve. As the valve has been leaking the water level would be filling higher (up to overflow) than stopcock would usually allow, this is why it would drop a couple of inches before the stopcock allows the valve to properly open.

What you will need to do is to replace the stopcock valve as it is not closing properly, water is trickling in and straight down your overflow to somewhere outside. I had to change my one about a year ago.

Pretty easy fix, but roofspace and darkness can make it a PIA

RunningMan

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#1567437 7-Jun-2016 20:07

It's a header tank for low pressure gravity fed hot water. It supplies cold water to the hot water cylinder. The outlet at the top is an overflow for if it over fills. This would happen of the ballcock or float valve is closing properly, possibly a hard washer or similar.

Water level will drop when you are using hot water faster than the tank can refill. A ballcock also needs to drop the water level a couple of inches before it gets maximum incoming flow, so if you are filling the bath, you'll see a drop in level.

If it takes a couple of hours to overflow, then water is just creeping past the ballcock washer slowly.

gregmcc

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#1567441 7-Jun-2016 20:08

it is simply a "header tank" basically the hot water tank (and whatever else is connected to the outlet) is fed cold water, if it is overflowing over the overflow pipe then the ball float valve is not shutting off correctly and stopping the flow of water before hitting the overflow, common fix is to bend the ball down slightly so it stops sooner, there are some drawbacks from this, it could already have been bent fracturing the arm, it may break when you try to bend it. More than likely it is not shutting off correctly because it's worn out.

It may be a better solution to simply replace the complete ball valve.

gzt

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#1567452 7-Jun-2016 20:24

The little rubber valve thing is a couple of dollars. Easy to fit a new one. From memory just unscrew the endcap and there it is.

The entire ball/valve assembly is around 50.

Imho water can get ugly fast. Get a plumber to replace the ball/valve unit and sleep well. Job done for 20 years.

richms

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#1567456 7-Jun-2016 20:31

It will also raise up a bit as the water in the tank expands due to heating, so it shouldnt be set to turn off the water too close to the overflow.

Richard rich.ms

wally22

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#1567471 7-Jun-2016 20:59

gzt: The little rubber valve thing is a couple of dollars. Easy to fit a new one. From memory just unscrew the endcap and there it is.

The entire ball/valve assembly is around 50.

Imho water can get ugly fast. Get a plumber to replace the ball/valve unit and sleep well. Job done for 20 years.

You also need to remove the split pin shown in the photograph to get the plunger out to replace the washer. You can reuse the split pin easily though. You seem to have a robust overflow system there too, thankfully.

IMHO these ballcocks are the best for long life, only needing a $0.50 washer occasionally but plumbers seem to 'have' to install an expensive new plastic one that doesn't last as long.

If you can't manage the repair then any handyman should be able to do it. Where are you? I could come over and do it or show you how if you want.

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#1567502 7-Jun-2016 21:24

If the water still overflows and the washer looks in good condition, it is possible for water to bypass the washer if the stainless nipple in the valve is loose. The nipple screws in from the inlet pipe side of the valve.

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#1567529 7-Jun-2016 22:19

Ok thanks, I will look into the "valve" ... ! Thanks a million!

wally22

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#1567536 7-Jun-2016 22:36

Found this blurry video that shows the procedure.

https://www.youtube.com/watch?v=mTQy27l7qDQ

Batman

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#1571703 14-Jun-2016 14:41

wally22:

Found this blurry video that shows the procedure.

https://www.youtube.com/watch?v=mTQy27l7qDQ

Thank you so muchly!

That was perfect, I did exactly what it said and I've done a DIY! [I'm a DIY fail usually]

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#1571722 14-Jun-2016 15:05

Bend the float down on it's support arm. That usually works.

Mike

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Batman

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#1571724 14-Jun-2016 15:07

MikeAqua:

Bend the float down on it's support arm. That usually works.

Not if the washer's buggered.

wally22

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#1571916 14-Jun-2016 19:56

joker97:

wally22:

Found this blurry video that shows the procedure.

https://www.youtube.com/watch?v=mTQy27l7qDQ

Thank you so muchly!

That was perfect, I did exactly what it said and I've done a DIY! [I'm a DIY fail usually]

Happy to help you sort out a situation and you learning something too.

Just make sure the arm is adjusted (bent gently) to allow a reasonably full tank of water to accumulate, a bit below the overflow. About where it appears in your photograph.

Then there shouldn't be any delay getting water from your hot taps.