Ball valve stuck.

[george121212]

Hi all quick question.
I have a header tank in the loft with an immersion heater in the bathroom.
Noticed no water at all coming from the hot water taps the other day.

Checked the header tank and the ball valve in the header tank was stuck in the closed position.
As I opened the lid without touching the ball valve it lodged itself open.
It has been working fine since.
(I had changed a cold water tap the previous week and turned off the cold water could there have been a air lock in the cold water supply to the header tank?)

My 3 questions
1) Is this a common problem, last week was exceptionally hot could this have caused it?
2) With it working fine does it need further action?
3) If it happens again and my immersion tank is empty, if the coil comes on is there a risk it the immersion tank could blow up?

thanks for your advice

 

[Hugh Jaleak]

1. Yes, its not unknown for ballvalves to stick shut, but the weather is unlikely to be the cause.
2. No, unless it happens again, or now sticks open slightly and starts to overflow.
3. No. The hot water cylinder remains full of water even if the cistern feeding it is emptied.

Air lock is unlikely with mains pressure water, probably just coincidence. Remember the valve remains shut most of the time unless water is being drawn off.

 

[george121212]

Hi Hugh,

Thank you for your quick reply. Certainly reassuring.
With regard to point 3.
The only reason I thought the tank could blow up would be due to the following scenario.

If the header tank stops feeding the cylinder with a stuck closed ball valve , no cold water getting to cylinder.
Following this if the the household uses the hot water taps the immersion will eventually run to empty.
The risk would be that the coil would be heating up an empty immersion when turned on? Could this lead to problems?

many thanks
George

 

[copea]

It's the header tank feeding the cylinder with cold water at the bottom which pushes the hot out of the top.
No water in = no water out.
What's in the tank stays there, so the situation you describe will not happen.

 

[Hugh Jaleak]

No, the cylinder is fed from the bottom and the water to the taps is drawn off from the top. (Unless you've a horizontal cylinder or a square tank, which is now quite rare.) Hot water rises, hence the arrangement, and therefore the cylinder will remain full of water even if the cold cistern feeding it is emptied. To empty the cylinder requires opening the drain off tap that (should!!) be fitted to the cold inlet at the bottom of the cylinder, or sometimes a spare tapping at the base if fitted.

 

[Nozzle]

It'll empty the pipe from the head tank down as far as the horizontal hot out the top of the cylinder. I'm not thinking too clearly, but what I can't answer right now is why it won't syphon itself empty until air gets sucked in at the bottom.

...which is perhaps what happens. The syphonic action stops, the water glugs back up the feed pipe and that ends the draining.

Nozzle

 

[george121212]

Thanks for the feedback guys this is reassuring.

Nozzle- I suspect it will siphon to the same level because the force of gravity becomes equal on the water in both pipes which is why it stays level at the horizontal hot out and feed pipe...?

 

[Steelmasons]

It'll empty the pipe from the head tank down as far as the horizontal hot out the top of the cylinder. I'm not thinking too clearly, but what I can't answer right now is why it won't syphon itself empty until air gets sucked in at the bottom.

Nozzle

Open safety vent will prevent cylinder from imploding.