Help please with central heating issue!

[Speeed Freak:)]

Any plumbers about?

The small tank in the loft ( header tank?) keeps over flowing, constant drip!

I've changed the ball cock but it still does it, the valve attached to the ball cock seems to function ok. If I empty some water from the tank within a day it's full and over flowing again.

Bleed all of the rads all ok

Any one help?

Thanks
Andy

[lewis]

Hi Andy, does it shut off fully if you hold it up by hand, if it does try bending the arm that the ball is attached to down towards the bottom of the tank or unscrewing it to make the arm longer. This will put more pressure on the ball valve and shut it off before it reaches the overflow. Hope this makes sense, Lew

[Speeed Freak:)]

Originally Posted by lewis

Hi Andy, does it shut off fully if you hold it up by hand, if it does try bending the arm that the ball is attached to down towards the bottom of the tank or unscrewing it to make the arm longer. This will put more pressure on the ball valve and shut it off before it reaches the overflow. Hope this makes sense, Lew

Tried that! Doesn't seem to make any difference, water just covers the ball, valve seems to shut off ok

[df-03]

on the main valve reduce pressure for 1 bar, hope would help.

[Speeed Freak:)]

Originally Posted by df-03

on the main valve reduce pressure for 1 bar, hope would help.

Not sure how too do that?

[lewis]

Hi Andy, sorry it didn't help. The only other thing i can think of is if you have a low pressure ball valve instead of a high pressure one. The low pressure one has a larger hole and if it fitted to a mains pressure pipe may be struggling to turn it off. Lew

[Speeed Freak:)]

Originally Posted by lewis

Hi Andy, sorry it didn't help. The only other thing i can think of is if you have a low pressure ball valve instead of a high pressure one. The low pressure one has a larger hole and if it fitted to a mains pressure pipe may be struggling to turn it off. Lew

No worries, thanks for the input!

[petemid8]

If you have a double feed vented system, the small tank in the loft is your feed & expansion tank. It does 2 things, feeds the central heating system with water if it needs it, and gives a space for the water in the central heating circuit to expand into as it comes on and warms up. So the portsmouth type float valve in the F&E tank should shut off when there isn't much water in the tank when the heating is off, perhaps only 20% full, not sure exactly.

So if your valve is working correctly and allowing enough free space in the tank to allow for expansion the only other thing I can think of is there is some sort of blockage in the feed pipe which is allowing the expanding water up the pipe into the F&E tank but not allowing it back down again? There shouldn't be any valves at all on the pipe from the F&E tank downwards to the heating bit.