Dripping Overflow

[John]

I have 2 overflow pipes at gutter height, one for the CH header tank and the other for the hot water cylinder feed tank. The one to the HW drips on a morning. I have been up and had a look at the tank, suspecting a new washer etc would be required and the water level was a good 3" below the overflow outlet pipe! I asked her indoors to run some hot water to drop the level and then I waited for the tank to refill. It did and the flow stopped as expected. There are no other tanks etc connected to this pipe so why does it drip, my first thought was condensation in the pipe but why doesn't the other one drip. Both tanks are side by side and the pipes are similar in length and run the same way so why one and not the other?

TIA

John

[daddyfreddy]

Unless of course you've got the pipes the wrong way round! ;-)

Did you check the CH tank while you were up there?

[John]

Yes, sorry I should have said that. I did check the CH header tank aswell and no problems there either.

Cheers

John

[Ken]

What happens is that when you use the hot water during the daytime, the ball valve shuts off and you think it is good. But it might need a few hours to leak and reach the overflow. At night when you are asleep the valve has all that time to leak and reach the overflow. Just change the valve and problem sorted.

ken

[John]

I also had the same thought as you. So this morning before I went to work knowing the house was going to be empty for 8 to 9 hours. I rigged up a pice of wood across the top of the tank and hung a piece of toilet paper over it so the ends were about 1/2" above the water level and also attached a pencil to it so the end was just touching the surface of the water. When I had a look when I got home, the toilet paper was bone dry and the pencil was still just breaking the surface. I have changed the washer whilst up there so I will wait till morning to see if it has helped but I am not anticipating it will have stopped, I think there is something else that is causing it.

Cheers

John

[john]

Possibly the pressure gets higher during the night and it leaks under the higher pressure.

John

[Stewart]

I share a supply pipe with my neighbour and find strange things can happen at night when they are home; for instance we can hear every time they have a shower as there is a corresponding water hammer. I also know that the water pressure is quite a bit higher during the night and this has caused me to have a similar problem to you. The higher pressure could be affecting one of the ball valves more than the other.

[Ken]

Stewart could well be right. At night when most people are asleep the pressure will be higher allowing the leak to occure. Another thing you should check is the expansion pipe from the hot water cylinder which should be over the same cistern. This is the safety device for when the hot water gets too hot and it then discharges. Check this over night, assuming you leave your hot water on all night.

ken

[John Rumm]

Is the CH feed and expansion tank mounted higher than the cold water cistern?

If so there is another possible failure mode: a small pinhole in the heat exchanger coil in the hot water cylinder would allow water from the central heating circuit to get into the domestic hot water. This would have the effect of slowly raising the level in the cold water cistern when no water has been drawn off for a period of time.

(the CH F & E tank should be installed such that it has a lower "head" than the main cistern to eliminate this possibility)

[John]

They are both on the same platform in the loft but with a 3" to 4" gap between them. Both bases are on the same level but as the CH tank is smaller the top of it is obviously lower than the hot water feed tank.

Cheers

John

[John]

The expansion pipe was cold this morning and the water level was as it was last night. I checked the levels etc. before anybody in the house ran any hot water. After reading your post Ken I cable tied an old sock on the end of the expansion pipe before going to bed and this morning it was bone dry, where it would have been wet if the water was coming up this pipe. Many thanks for all your advice/suggestions chaps but I really think it is something other than the water level rising in the tank. It's not a constant drip,drip,drip... like you would expect if it was a water level rising problem but a drip every minute or so. The annoying part is that the overflow pipes are directly above the back door, so if you get the timing wrong you get a drip of cold water on your head when entering or leaving the house. One last thing I am going to try, is to cut the pipe in a convenient place and put a bucket under the end from the tank and see which end drips then. I will of course reconnect the pipe after my experiment is over.

Cheers

John

[Ken]

Another thing to check for John, is condensation. Is the leaking overflow pipe in copper and perhaps the other pipe is plastic. The cold exterior air blowing up the copper pipe could be condensing once it hits the warmer pipe in the loft.

ken

[John Rumm]

That's ok then, scratch that option!

[john]

A house near to me has had a hose attached to a WC overflow pipe for around

20 years. Could have wasted an enormous amount of water. Odd that ball valves mystify so many people - at this house the owner had to go up a ladder - connect the hose - clip the hose to the wall and lead it to a rainwater hopper. However, he saved about 5p on a ball valve washer.

John

[a.n.other]

Try lagging the overflow with pipe lagging. Could reduce condensation build up.