Another Hot Feed/Expansion tank heating up question

Graeme2 · 15 Dec 2006

Hello,

I've seen other people's posts on here, but they don't appear to be quite the same as mine.

My expansion tank is being warmed by water from the overflow. I can hear it dribbling in through the overflow, so it isn't submerged in the tank.

By elimination I now know that it only happens when heating my water cylinder. Both the radiators and cylinder heat up well. I've tried turning the pump down from 3 to 2, it slowed the water going into the loft, but it's still happening.

Layout of the system: The expansion tank is in the apex of the loft space about 3m about the hot water cylinder/pump which is on the top floor both of which are about 50cm above the boiler which is high on the wall in the kitchen downstairs.

Any advice would be greatly appreciated.

Graeme

JPC · 15 Dec 2006

just started recently or always done it ?

Graeme2 · 15 Dec 2006

It just started recently.

Changes that I've made to the system are new pump (facing the right way). Some fernox restorer for a week, then drain and refill with some fernox inhibitor. I've also changed 2 radiators (changing some pipe work).

On the cylinder side, pretty much only the pump in the loop has changed.

The only other thing I can think of is that the water level in the F&E tank is quite high (not overflowing). Could the high water cause extra pressure that brings it into the cycle? I wouldn't have thought about 3m vs 3m 20cm would cause that.

Thank you

Alfredo · 15 Dec 2006

Try pump on speed 1..and see what happens. If the system still works OK and the pumping over stops..then its job done. I know we all call it a pump, but its not a pump at all..its a circulator, and as such does not necesarily have to be that powerful.

The system might not work properly on 1, or the boiler might kettle, but try it first and come back to us.

Alfredo

Graeme2 · 15 Dec 2006

Thank you, I've switched it to 1, and it doesn't seem to be running into the loft any more. I'll watch it, and also make sure the house continues to stay warm.

New house, the system was incredibly dirty and although set to 3 I think the old pump was about to die anyway. So when replacing a pump, I have learn't not to just duplicate the old pump settings.

Thank you very much for the advice.

JohnD · 15 Dec 2006

I understand you mean that water is coming from the vent pipe (the 22mm copper pipe that is bent over the F&E tank). The overflow is the pipe that leads from near to top of the tank and discharges outside the house.

How high above the tank is the bend?

You only need about two inches of water in the F&E. If you can, adjust the float so that it stops inflow when the float is at two inches; and bale out the tank to bring the water level down to that point.

Let us know what sort of sediment you find in the bottom of the F&E. Preferably bale it out, and sponge up the residual mud. Do this with the float valve tied up to prevent new water getting in.

You say the system seems dirty. This will get worse if it has been pumping over, since this brings in aireated waterthat encourages the radiators to rust internally.

It may help to give it another chemical clean and flush if it does not seem to be fully clean.

Dukie1977 · 15 Dec 2006

By elimination I now know that it only happens when heating my water cylinder.

Why would pumping over occur only when heating the hot water cylinder?

JohnD · 15 Dec 2006

Dukie1977 said:
Why would pumping over occur only when heating the hot water cylinder?

The pump is running flat out and trying to force the entire flow through the cylinder coil. Perhaps the pipework has been necked down to 15mm. Perhaps there is a service valve stuck or partially closed. Perhaps the motorised valve is stuck or damaged. Perhaps there is a sediment clog.

Graeme2 · 15 Dec 2006

Yes sorry, the vent pipe. The bend is about 30cm above the tank, about 45cm above the water level. I think the float is bent up from me tying it up so often, I'll adjust it down at some point.

The system is quite clean at the moment, I've done quite a bit of cleaning of the system, flush several times, then fernox for a week (advised by plumbing merchant when he saw the state of my old pump), and then flushed it through serveral times again. So at the moment it's quite clean and a nice new pump. One of the reasons I thought Alfredo's simple solution to be quite good. Before all the cleaning and while still on the old pump, I'm sure the flow was incredibly bad. So putting the new pump in after the clean and setting it to 3, was probably a bad idea. So it's now on 1 and all appears to be well.

Directly after the cylinder coil the pipe work does drop down to 15mm. As I said before all the radiators are working well, and the water in the cylinder is heating. I just noticed condensation in the loft recently and traced it down.

Thank you again.

JohnD · 15 Dec 2006

The higher the vent pipe goes before it bends down, the better, as the pump has to lift the water that high before it can be pumped over.

Dukie1977 · 16 Dec 2006

JohnD said:
The pump is running flat out and trying to force the entire flow through the cylinder coil. Perhaps the pipework has been necked down to 15mm. Perhaps there is a service valve stuck or partially closed. Perhaps the motorised valve is stuck or damaged. Perhaps there is a sediment clog.

Thanks JohnD for your answer, they teach me bot all at college. So basically any restriction in the pipework could be the cause.

My understanding now is as follows: When the pump is operational, the water is pushed through the vent pipe because the flow is insufficient through the restriction. When the heating is on, there is sufficient flow for this not to happen. Please correct me if i'm wrong, and cheers again.

Rich

DP · 17 Dec 2006

Pump over will NEVER take place if plumbing is correct. To take the vent to the moon and back, to tinker with pump speed etc is futile. It is plain and simple a case of incorrect plumbing.

If by manipulation of vent pipe, pump over is eliminated when system is running, the problem will still be there on start up. Water will spurt out of the vent every time the pump starts.

I suspect this was a gravity hot water system that has been converted to be fully pumped. Pump over is taking place because the pump is between the feed and vent pipes. Moving the pump to the cprrect position will stop it pumping over.

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Another Hot Feed/Expansion tank heating up question

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