Heating expansion tank overflowing

Postby martinbaird » Fri Sep 19, 2008 7:23 pm

Hi. I have a heating system expansion tank that is (nearly) always overflowing. It is not the obvious problem of a faulty or badly adjusted ball valve, this can be tied up and the overflow continues.
I can only think that water is being introduced into the heating system from the mains supply. Is it usual to have a valve to fill the heating system from the mains supply and could this be leaking? The water and heating system is quite old.
Perhaps I am being optimistic but is there a usual location for such a valve?
Thanks for any help. Martin
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Simply Build It

Postby nitro23456 » Sat Sep 20, 2008 1:24 pm

If you have tied up the ball valve and the water continues to flow from the mains feed, it is just that - a faulty ball valve wich is probably gunged up and can be replaced for £5 or so (its probably just the diaphragm but its easier to replace the whole thing).

The only other place the water can be entering the feed and expansion tank is, as the name suggests, the expansion pipe. It could be doing this for a whole host of reasons and you need to provide more details.

The expansion pipe is the hook shaped pipe that enters the F/E tank over th top, normally through the tank lid.

Start by finding where the water is coming from and tell us more. Does it stop with the stopcock off? only happen when the heating is on? pump on? do you have a hot water cylinder? etc etc
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Postby htg engineer » Sat Sep 20, 2008 2:32 pm

But the only way water could be introduced from the mains supply would be, a faulty ball valve, or a hole in the cylinder/tank coil.

When the system is cold, what is the water level like in the tank ? as the name suggests, feed and EXPANSION there needs to be room for expansion. If the water level is too high when cold it will overflow when the heating is on.

htg engineer
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Postby Steve the gas » Sun Sep 21, 2008 6:02 am

My money'son the tank coil -pinholed/corroded
Steve the gas
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Postby plumbbob » Sun Sep 21, 2008 12:35 pm

You do mean the expansion tank is overflowing onto the ground outside the house don't you?

If so, I'm with Steve the gas on the cause.
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