Heating f&e pipe flowing hot water

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I have a gravity fed heating system oil heating.
When heating is fired up, the expansion pipe flows hot water into small feed tank until heating goes again.
Was thinking of extending expansion pipe a few feet in the hope it would stop,
Would this stop the water flow into tank?

I notice the copper cylinder return pipe which is also connected to cold feed is very hot , as hot as the flow pipe going to the coil.

I'm thinking a blockage around this area would that be feasible?
 
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Assuming it's plumbed boiler - open vent - cold feed - pump, it's likely to be caused by blockage between the open vent and cold feed connections.
 
Send a picture of the water level in the F/E tank.

Get a magnet, place it near the pipes if the magnet sticks to the pipe it will tell you that you've got a blockage.

Have you changed the pump speed recently?

How long has this problem existed for?

After fixing the issue you will need to add inhibitor after topping up as by now you probably have massively oxygenated the CH water.
 
Thanks for reply, although no pic of f&e water level ,I would say it's half full.
Have pics of copper cylinder with cold feed.

it's my sons house who moved in last July and to be honest it looks like a pretty new oil boiler been fitted in outhouse with a mangnaclean filter fitted.
Tried a magnet at copper cylinder cold & vent pipes but nothing seems to be there.
 

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Have pics of copper cylinder with cold feed.
If you mean the cold feed to the cylinder from the CWST (the bigger tank in the loft) that's not the problem. The problem is on the primary circuit. Where do the open vent and cold feed join the circuit? Is the pump on the boiler flow or return? A hand sketch would be useful if you can't get a photo.
Nothing to do with the overpumping, but the pump installation isn't ideal. Better to bring the power lead in from underneath, can be corrected by removing the 4 Allen bolts and rotating the head 180°, as discussed in a recent thread.
 
Sorry my explanation wasn't good, in the photo, the pipe at bottom of cylinder with the gate valve on, is the primary heating return coming out from the heating coil which in turn is connected to the cold feed coming from small f&e tank in loft.
The higher connection coming out of cylinder is the primary flow from the coil which is teed into the vent pipe for heating circuit.
Cheers
 

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There are questions you haven't answered

How long has this problem existed for? If it's long-term or a new installation, maybe the plumbing is all wrong.

Where do the open vent and cold feed join the circuit? Is the pump on the boiler flow or return? A hand sketch would be useful if you can't get a photo.

It sounds like the cold feed is to the boiler return. If the pump is on the flow, that went out of fashion in the 1980s, as it causes seesawing, bringing aerated water into the system. But would be unlikely to cause pumpover. Hence the question about the layout.
 
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How long has this problem existed for? If it's long-term or a new installation, maybe the plumbing is all wrong.?

Honestly don't know as my son only moved into house july 24.

The boiler doesn't look that old and has a magnaclean fitted and pump fitted on same pipe so I am assuming that pump on return, not really know until I'm there again and firing boiler up.

Yes cold feed piped into return at the copper cylinder and vent teed into flow also at cylinder ,see pics
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Flow & return from boiler > to under floor and join cold feed and flow vent pipe in loft. > to copper cylinder were both flow & return connect to heating coil > then under floor and connect to radiators both upstairs and down.
Cheers
 
Flow & return from boiler > to under floor and join cold feed and flow vent pipe in loft. > to copper cylinder were both flow & return connect to heating coil > then under floor and connect to radiators both upstairs and down.
Cheers
Is the vent taken off the boiler flow pipe? That could explain the overpumping as the pressure at that point will rise due to the headloss in the rads or cylinder.
What speed is the pump on? Should be lowest at which everything works, that might reduce or cure it.
If not, relocating the vent to just before the cold feed connection would do it. But might not be easy, depending on the house layout.

Edit - another option, move the cold feed to just after the open vent.
 
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This thread was about a similar problem, might help
 

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