5 Jan 2010
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West Glamorgan
United Kingdom
overflow from the header tank of the cylinder on my central heating system, overflows in the evenings and mornings,
the boiler is a baxi 552 back boiler and the cylinder has a header tank attached to it with a seperate f&e tank above it, the overflow stops when i draw of hot water. any ideas why ?
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Float valve in cistern passing. Over night when no water is used it allows the level of the water to reach the overflow. When you open the tap the water level drops and it stops overflowing. The float valve needs to be repaired or replaced..
Thanks for your reply, have checked the ball /float valve there is a slight drip but nothing to be concerned about once every 10 seconds, the water level is about 25mm from the mouth of the overflow in normal working conditions, cylinder is extremley hot, boiler seam to be working fine even though its about 25 years old.
even a small drip every few seconds can build up over time and cause an overflow eventually.

Depress the float valve arm until it gets higish and then see if the float valve shuts off properley.

If this is ok, possibly condensation/cold weather/ice erc on the overflow pipe from outside may be dripping and seem like a fault...??
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I agree a small amount of water can build up but the amount of water that overflows does not relate to a drip, as it pours out, when i have looked into the top of the cylinder it look as if there is a swirl of water coming from the cylinder into the header tank from the pipe that is on the bottom of header tank , also when i have looked into the F & E tank there is, what looks like a white scummy covering to the surface of the water ?.
Could it be that it is overheating.
The hot water cylinder coil may have pinholed (old age) and as youe hesder tank is HIGHER water level than your cold water tank, your cold water tank if overflowing instead.

Is the header tank constantly filling?

You say the cold water tank's outlet at the bottom (from the hot water tank) is filling up??
ok! the cylinder has a tank attached to the top of it as if it is a combination and the cold tank is above this, there are four pipes, on the one that is attached to the cylinder. cold water feed that has a ball valve and there is a over flow pipe and there is a pipe at the bottom of this below the water, that is attached to the cylinder if that makes any sence. and there is also one that is attached to the expansion pipe.
Sorry the header tank is filling up but only when water is not being drawn off, normaly the water and heating are on all the time, as i cant have hot water on its own.

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