another header tank problem

[leela]

HELP!! I have a problem regarding a immersion heater and a header tank. The problem seems to be that water is expanding through the cold water inlet, filling the header tank and then overflowing. I have replaced the element and stat, the temp is set to 60 celcius and the tank and pipe work is in a state of good repair. Can anyone explain to me why this is happening and what can be done to resolve the problem? the system is not being overheated, the header tank is plastic and the ball valve has been renewed. cheers leela

[Bob Mannix]

The most common fault that causes this is that the ball on the ball valve in the header tank is set too high. The tank is intended as an expansion tank but there has to be enough capacity between the level when cold and the overflow. Bend the ball valve arm down towards the water a bit, then run off some hot and see if the problem persists.

The cycle is:

water cools and contracts ball valve opens and tops up tank as water level drops water heats, expands and overflows

cycle repeats

This is if all you have is a header tank, hot water tank and immersion heater. If you have central heating that heats the water through an indirect coil in the hot water tank, there may be other, more serious, explanations requiring more drastic action! I am sssuming not for now..!

[leela]

[leela]

[tinnews]

Almost certainly not due to expansion, water doesn't expand all that much. You've got some sort of flow back into the header tank.

A faulty valve on a washing machine (or similar) that has hot and cold feed might cause something like this as the cold mains pressure will be quite sufficient to push water back through the hot water system.

[TheScullster]

"leela" wrote

The issue that Bob is probably referring to is a failure of the coil inside the hot water cylinder. This allows water to leak from the primary circuit (usually shared with central heating system) into the hot water cylinder. If the pressure on the primary side is greater than in the h/w cylinder water will back-fill your domestic water storage tank. This is sometimes accompanied by dirt or discolouration of the hot water supply, depending on the state of the water in the primary circuit.

Do you have a small header tank in the loft feeding the primary circuit? If so, is the level of water in the small tank above the level in your main water storage tank? If it is, then this may generate sufficient pressure on its own to back fill the main storage tank.

Hope this is all clear

Phil

[Roger Mills]

The potentially serious problem to which Bob was referring was the possibility of a leak in the indirect coil - allowing water to flow from the boiler loop into the DHW system. There would have to be a differential pressure for this to occur - requiring the level in the small tank to be

*higher* than that in the main tank.

The fact that the water in the main header is warm without the boiler running suggests to me that your problem is just one of simple expansion - which will be fixed by adjusting the ball valve.

But do also check that the hot and cold are not connected together via a faulty washing machine valve, as someone else has suggested.

[Guy King]

The message from [e-mail] contains these words:

Unlikely on a washing machine as they are designed so that the hot and cold empties into the soap-tray from seperate holes - the whole tray would have to fill with water /and/ hold pressure for this to happen.

[John Stumbles]

I had a problem klike that which turned out to be a leak in the block of a monobloc mixer tap fed with cold from the mains and hot from the gravity-fed HW system. You could actually hear it rushing in the tap body, and the water in the storage tank was warm and you could see convection currents as the warm water rose from the outlet of the tank.

[Dave Plowman (News)]

Yes - I'd guess they are all designed to prevent potable and non potable water mixing.