I know virtually nothing about how central heating systems work so would be very grateful for some help as I am trying to help a friend out. She has two overflow pipes coming out the side of the house. The one that comes from the expansion tank is overflowing constanly with hot water. I got up in the loft and had a look. The expansion tank is full of hot very murky (dark brown) water. There is a pipe leading into the expansion tank which I think comes from the hot water cylinder in the bedroom below. Hot water is gushing out of this pipe at a rate of knots (Like a tap turned full on) and filling up the expansion tank causing it to overlow via the overflow pipe. Im not sure how the ballcock should look, but it is well below the water level. If you turn the hot water off at the switch above the boiler downstairs, the hot water straight away stops filling up from the pipe coming from the hot water cylinder. If you turn the hot water back on, it starts up again. Whats going on?
overflow from expansion tank
- Thread starter chris99
- Start date
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A classic example of pumping over through the vent pipe. If you alter the speed setting on the pump, it may diminish or even stop this. Typically a pump will have 3 speeds, so if it's on 2 or 3, turn it down.
Probably this won't solve the problem, so you need to have the pipework altered to prevent it. chances are that a great deal of corrosion has occurred as a result of the pumping over, so the whole system may need flushing and chemical cleaning.
Unless you want to embark on a rather steep learning curve, you'd better get some professional help with all this.
Probably this won't solve the problem, so you need to have the pipework altered to prevent it. chances are that a great deal of corrosion has occurred as a result of the pumping over, so the whole system may need flushing and chemical cleaning.
Unless you want to embark on a rather steep learning curve, you'd better get some professional help with all this.
A bit of confusion over what's where I think. Both the heating expansion and big cold water storage tanks have vent pipes over them. The CWS feeds the hot water cylinder and cold taps.
It sounds like the vent pipe from the heating (not hot water tank) is "pumping over " when the boiler and therefore pump is on. This is usually caused by bad system design or a recent problem like a pipe getting blocked. But it pumps water from the heating system, so the exp tank shouldn't overflow.
Presumably the float valve isn't leaking, so the water is coming from the CWS. This means that the coil of pipe inside the hot water cylinder, which boiler water goes through to heat the HW, is leaking. That allows water from the CWS into the heating. Normally the exp tank would just overflow - your pumping-over is additional!
Even with the boiler/pump off, you would expect the exp tank to overflow, though it may be slower. If it doesn't, you have a mystery, why should the exp tank overflow! Answers on a postcard!
It sounds like the vent pipe from the heating (not hot water tank) is "pumping over " when the boiler and therefore pump is on. This is usually caused by bad system design or a recent problem like a pipe getting blocked. But it pumps water from the heating system, so the exp tank shouldn't overflow.
Presumably the float valve isn't leaking, so the water is coming from the CWS. This means that the coil of pipe inside the hot water cylinder, which boiler water goes through to heat the HW, is leaking. That allows water from the CWS into the heating. Normally the exp tank would just overflow - your pumping-over is additional!
Even with the boiler/pump off, you would expect the exp tank to overflow, though it may be slower. If it doesn't, you have a mystery, why should the exp tank overflow! Answers on a postcard!
I was wondering the same thing, but couldn't think of anything clever, so kept schtum. The idea of water leaking from DHW side seems improbable, although possible, but as ChrisR says it's nothing to do with pumping over.
The overflowing might be the result of a partial blockage of the feed pipe, so water would not replace that pumped over fast enough. But something must replace water pumped over - could this be air already in system or sucked in by sub-atmospheric pressures upstream of pump?
As ChrisR also pointed out, there is also the question of whether the float valve is leaking. If it was that would explain the excess water but then the overflowing would continue when pump was not running.
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first post says it is overflowing constantly so I would say you're right with the ballvalve. On the pumping over side of things if you turn the pump down and it still overflows slightly, increasing the height of the vent pipe will fix it, although in the longer term you need some pipework reconfiguration.
I am sorry, but I think that you are all missing the point, it is not the vent pipe which is causing him the problem. It is the pipe which allows the F & E tank to create the pressure in the heating system (the pipe comes of the flow to the HW tank and is the one which allows the re-filling of the system.
The water which should be circulating around the cylinder coil is coming up into the F & E tank for some reason and the overflow from the overflow pipe is probably condensation from the heat created in the tank.
I have a similar problem and managed to sort it partly by changing the stat on the hot water tank which was not working properly and allowing the tank to get too hot. However I still have the problem of the circulating water coming up into the tank, not so much now. It always seems to be just as the pump starts/mid position valve opens to give heat to the HW coil.
Could the coil be blocked? Or is it just that the pump is running too hard if it is only supplying the HW and not the CH. Then the coil slows down the flow and the only way out for the water is up into the F & E tank.
In my case it is definentaly not the vent pipe as it is cold and I have watched the water come up from below.
I hope this makes some sense.
Andrew
The water which should be circulating around the cylinder coil is coming up into the F & E tank for some reason and the overflow from the overflow pipe is probably condensation from the heat created in the tank.
I have a similar problem and managed to sort it partly by changing the stat on the hot water tank which was not working properly and allowing the tank to get too hot. However I still have the problem of the circulating water coming up into the tank, not so much now. It always seems to be just as the pump starts/mid position valve opens to give heat to the HW coil.
Could the coil be blocked? Or is it just that the pump is running too hard if it is only supplying the HW and not the CH. Then the coil slows down the flow and the only way out for the water is up into the F & E tank.
In my case it is definentaly not the vent pipe as it is cold and I have watched the water come up from below.
I hope this makes some sense.
Andrew
I am sorry, but I don't think you really know what you're talking about. We know which pipe the water is being pumped out off (known as the CH vent pipe but not the same as the DHW vent pipe). As for the overflow being condensation, that doesn't really fit what the poster has told us.Andrew said:
I was trying to make a distinction between the vent pipe which comes direct from the boiler (in a boiler overheat situation) and the pipe which comes into the bottom of the tank from the flow on the HW circuit which feeds the coil.
My F & E expansion tank overflow pipe had quite a lot of water coming out of it just from condensation, water level in tank was a good 5-7cm below the outflow and the water in the tank was very warm, nearly hot.
If you do not think this person's problem is caused by condensation, then can you hazard a guess at my problem?
My apologies if my post appeared abrupt in any way, you can blame the typed word for that rather than speaking to somebody face to face
My F & E expansion tank overflow pipe had quite a lot of water coming out of it just from condensation, water level in tank was a good 5-7cm below the outflow and the water in the tank was very warm, nearly hot.
If you do not think this person's problem is caused by condensation, then can you hazard a guess at my problem?
My apologies if my post appeared abrupt in any way, you can blame the typed word for that rather than speaking to somebody face to face
Hello ChrisR,
I have tried to start a new thread with a diagram, but no joy. Just seen another post, could it be that the level in the F & E tank is too high. Seen a post which says that the level of water should just be enough to cover the pipe, is this true?
Last post in this thread and then a new one.
Thanks
Andrew
I have tried to start a new thread with a diagram, but no joy. Just seen another post, could it be that the level in the F & E tank is too high. Seen a post which says that the level of water should just be enough to cover the pipe, is this true?
Last post in this thread and then a new one.
Thanks
Andrew
Water will take the path of least resistance...if it is going up the feed rather than the vent then there is some blockage somewhere I would guess between feed and vent. I'm not sure I understand your problem completely though, I'm not 100% sure which tank is overflowing and the relevance of the cylinder stat.
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