Heating hot when HW only selected. Can I fit a 2 port valve?

[*ashy*]

Hi people. I hope you can help me.

We have an old primatic heating system. Gravity fed for the hot water and pumped for the Central heating.

The problem is that the radiators still get hot when only hot water is selected on the timer.
It seems they are being heated simply by convection as they still heat even with the water pump disconnected. If I close the manual valve on the pump then the radiators don't get hot, but this is a pain having to do this.

My question is, can I just fit a 2 port valve in place of the manual valve?

If so how is it wired, do I just wire to the same terminals as the CH pump, so they both activate together when the CH is selected to come on?

Also is it normal for this to happen with gravity systems? I know the pump is on it's way out as it doesn't heat the downstairs radiator unless I turn the upstairs ones off. It just seems odd that the radiators get hot upstairs without being pumped.

Your help is much appreciated.

 

[ChrisR]

2 port yes. Wire pump through its auxilliary switch so pump comes on when valve has opened. Swing check valve should work and is cheaper!

http://www.bes.ltd.uk/products/graphics/7518.gif

 

[*ashy*]

Ok sounds good, which side of the pump do I fit the check valve, inlet or outlet?

Our pump is vertically mounted, (I.E the inlet and outlet runs from top to bottom).
How do I know which is the inlet side of the pump and which is the outlet side. All I know is that the manual shut off valve is at the bottom of the pump.

Sorry about my crude image but this is the pump as it is:

 

[ChrisR]

Pump will have an arrow on it - though makes vary. It could be in the flow OR the return.
The swin valve will only work in upward or horizontal flow. Downward, it would fall open. Doesn't matter which side of the pump it goes.

 

[*ashy*]

Ok thanks. Let me just get this straight in my head then. If the valve has to go upwards this means that the pump has to pump upwards too so that the valve opens when there is flow from the pump. Water cannot come back the other way as the valve will close?

Is it not possible that hot water would still be able to rise up through the pump and push the flap up still?

 

[dal5band]

It's small weight on a hole so convection will not push it up but you may get a small amount of hot water going through because it's not a tight closure, not enough to heat a radiator.

I would think it would need to be within a few feet of the pump so the pressure will open it .

 

[*ashy*]

Ok thanks mate. I may just go with the 2 port valve anyway to be sure. I'm replacing the pump aswell so don't wanna have to draindown the system twice if it doesn't work.

I can get the 2 port valve for about £20.

Thanks.