Ok - been in my house a year and its got a new Potterton boiler, with
std hot water tank, with expansion tank in the loft. I have always had a
leaking over flow but if was pushed to the back of my mind while I ahd
an extension done.

Anyway - know its doing my head in.

I ahve checked its not the any corroded parts n the expansioin tank,
causing water to be filled up even though the counter balance is down.

What seems to be happending taking taoday as an example. Not central
heating on - and we have on timer - several hours in morning and
slightly more at night.
So today its just hot water being timed on - and hence am getting
overflow, upthrough the expansion tank and hence into overflow and then
coming out the pipe at the side of my house.

What has caused this - air in the system?

Advice please so I can cur ir

Scott

"Scott" wrote in message
...
Ok - been in my house a year and its got a new Potterton boiler, with
std hot water tank, with expansion tank in the loft. I have always had a
leaking over flow but if was pushed to the back of my mind while I ahd
an extension done.

Anyway - know its doing my head in.

I ahve checked its not the any corroded parts n the expansioin tank,
causing water to be filled up even though the counter balance is down.

What seems to be happending taking taoday as an example. Not central
heating on - and we have on timer - several hours in morning and
slightly more at night.
So today its just hot water being timed on - and hence am getting
overflow, upthrough the expansion tank and hence into overflow and then
coming out the pipe at the side of my house.

What has caused this - air in the system?

Advice please so I can cur ir

Scott
You have a leak in your hot water cylinder allowing the hot water, under
pressure from the tank in the loft, to pass into the central heating system
and overflow the tank in the loft.

A friend of mine had this fault a couple of years ago. When hot water
storage tank was replaced problem went away. Also found that at least two of
the pipes connecting to the tank, at the back, were leaking at the "welds",
and causing considerabledamage to chipboard flooring and plasterwork.
Plumber said it was because is was the cheapest, nastiest storage tank with
the thinnest copper he had ever seen.!!! Suggested that it probably had no
sacrificial anode (zinc coil ?) fitted.

So today its just hot water being timed on - and hence am getting
overflow, upthrough the expansion tank and hence into overflow and then
coming out the pipe at the side of my house.

Can you just be clear that this is the feed and expansion tank for the
boiler circuit and not the cold water cistern for the hot water cylinder?

If so, and there is no water coming through the valve, then I agree with the
other poster that your hot water cylinder heat exchanger is holed. However,
it could also be someone limited in understanding setting the standard water
level too high (it should be very low in the tank), so it is unable to
accept expansion. When cold the water level should be very near the bottom
of the tank. When the system heats up, the water level rises, but not up to
the overflow.

In any case, you might want to remove the F&E tank and replace with a sealed
pressurised system. You'll still need to replace the hot water tank, though,
if it is bust. Try asking about what type to replace it with if you want to
see everyone groan.

If you only have one tank and it is the main cold water feed, and you don't
have a Primatic abomination, then you probably already have a sealed
pressurised system. In which case, the overflow is either caused by:

(a) the water level being too high, so is unable to accept the expansion of
water in the hot water cylinder when it heats up. The water level should be
fairly high in the main tank, but still with expansion room.

(b) again a leak in the heat exchanger. This would be coupled with a
tendency to rapidly lose pressure on the primary circuit, requiring frequent
topping up.

Christian.

In an earlier contribution to this discussion,
Scott wrote:

Ok - been in my house a year and its got a new Potterton boiler, with
std hot water tank, with expansion tank in the loft. I have always
had a leaking over flow but if was pushed to the back of my mind
while I ahd an extension done.

Anyway - know its doing my head in.

I ahve checked its not the any corroded parts n the expansioin tank,
causing water to be filled up even though the counter balance is down.

What seems to be happending taking taoday as an example. Not central
heating on - and we have on timer - several hours in morning and
slightly more at night.
So today its just hot water being timed on - and hence am getting
overflow, upthrough the expansion tank and hence into overflow and
then coming out the pipe at the side of my house.

What has caused this - air in the system?

Advice please so I can cur ir

Scott

I assume that it's the feed and expansion tank which is overflowing? Is the
level in the main cold header tank (for the hot water system) higher than
that in the f&e tank? If so, as others have suggested, the likely culprit is
a leak in the internal coil in your hot water cylinder - allowing the
primary and secondary water to mix, and forcing secondary water, at slightly
higher pressure than primary, into the primary circuit. If this *is* is
problem, it means replacing the hot water cylinder.

As someone else has said, it could *just* be caused by the ballvalve in the
f&e tank being set too high - so that when the system heats up and expands
it overflows - and when it cools down and contracts, fresh cold water is let
in by the ballvalve. This is the first thing to check, but is probably *not*
the problem, unfortunately.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Ok - excuse my ignornace - 2 tanks in the lost.

One is the cold water feeder - its far larger than the expansion tank -
which is quite small and the one that is creating the drip on the
outside of my house.

The colder water tank eg - fills the toilet up etc when pulled

Second floor - hot water cylindar

Note - expansion tank only over flows durring the timing when the hot
water is on.

So - the cold water feeder tank - that level should be quite high?

Scott

Note - expansion tank only over flows durring the timing when the hot
water is on.

So - the cold water feeder tank - that level should be quite high?

The big tank should be fairly high, but well below the overflow.

The small tank should be very low. Ensure that the valve only admits water
when the tank is approaching empty.

If these are OK already, then still suspect the heat exchanger. Weird stuff
can happen with pinhole leaks, which may only show themselves when certain
temperatures appear on the different sides of the exchanger. It can only get
worse, though, and may start leaking continuously.

Christian.

Cheers, I think I may change the ball valve in the over flow to prove
that - as have one spare and go from there. Think its the hot water tnak
though.

Scott

In message , Christian
McArdle writes
Note - expansion tank only over flows durring the timing when the hot
water is on.

So - the cold water feeder tank - that level should be quite high?

The big tank should be fairly high, but well below the overflow.

The small tank should be very low. Ensure that the valve only admits water
when the tank is approaching empty.

but presumably the level needs to be above the level of the outlet
connecting to the heating system?


--
dave @ stejonda
Bring culture back to NTL.
http://www.performance-channel.com/

In an earlier contribution to this discussion,
Scott wrote:

Cheers, I think I may change the ball valve in the over flow to prove
that - as have one spare and go from there. Think its the hot water
tnak though.

Scott

Do you have a stop tap in the supply pipe to the f&e tank? If so, turn that
off for a day or two and see whether the problem is still there. If it *is*,
it is almost certainly the hot tank.

[Don't forget to turn the tap on again after the experiment!]
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Ok - tonight I have checked the levels and made sure the main cold tank
in loft - the level is higher than the expansion tank. In the morning I
will go and see how far the expansion tank ahs risen.

I wont hold my breath.

Scott

Ok - tonight I have checked the levels and made sure the main cold tank
in loft - the level is higher than the expansion tank. In the morning I
will go and see how far the expansion tank ahs risen.

Have you turned off the F&E water supply? That way you can be sure than any
extra water must have come from the DHW system.

Christian.