Central heating/hot water - expansion tank - and over flow - help and advice needed

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

Reply to
Scott
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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.

Reply to
Ian Middleton

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.

Reply to
Christian McArdle

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.

Reply to
Set Square

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

Reply to
Scott

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.

Reply to
Christian McArdle

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

Reply to
Scott

In message , Christian McArdle writes

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

Reply to
NoSpamThanks

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!]
Reply to
Set Square

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

Reply to
Scott

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.

Reply to
Christian McArdle

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