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Hot water spilling back to Atic Heating header tank

Postby 9884booth » Tue Dec 07, 2010 7:18 pm

Help, I have purchased a house that has a traditional floor mounted boiler, 6 radiators and a immersion heater with motorised valves to operate heating, water or both.
There is a small cold water tank that gravity feeds the heating system if a radiator is drained or the system emptied.

Some of my radiators are not getting too warm, I've played around trying to balance the radiators with no sucess.

I noticed that the heating pump (grunfos) was set at position 1 so I increased to 3. Immediately all the radiators became hot and all seem fine.

I then noticed when in the atic that hot water was spilling back into the top of the cold water header tank so the tank was acting like a radiator in my attic.

I turned the pump to 2, no difference, I then turned to 1 and the spill back stopped, but 2 of the radiators don't get very warm again.

Can anybody advise how I fix this? The pump is in the airing cupboard immediately below the cold feed tank (about 6-8ft below).

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Postby DEEARR2 » Wed Dec 08, 2010 11:39 am

Sounds like the expasion pipe (the one that is spilling into the tank) is incorrectly connected to the system. Ideally this pipe should enter the system on the draw side of the pump not the discharge side. A small pipework alteration would cure this and allow the pump to exert its capacity into the system.
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Postby 9884booth » Thu Dec 09, 2010 6:48 pm

I've checked the pipework and 15mm cold feed and 22mm overflow to the feedtank are both just before the suction side of the pump. Pump is installed right way around too pumping upwards and away from these two pipes.
All I can think of is some debris on the pump suction restricting flow through the pump and causing pressure on the inlet side of the pump and so pushing hot water up the overflow to the Attic tank.

Does it make sense or is there something more obvious?
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