Strange pump connected to HW cyl?

[Andy W]

Hi,

I have just moved house and am getting to grips with how everything is set up. While checking out the HW/CH system ( and getting rid of life-expired tank lagging) I found a Grundfos pump which looks like a CH pump but slightly longer. Unless I am mistaken the inlet of this pump is from some kind of cold supply and the outlet pumps straight INTO the side of the HW cylinder near the bottom. I'm quite sure it is going into the cylinder not the coil as you can easily flex the flange joint.

The pump is supplied from a fused switched outlet. On turning it on, nothing happened because the pump was jammed. Freeing the pump, it burst into life and made lots of air/water noises then settled down.

So what is this all about? Any ideas why one would want to pump cold water into the HW cylinder?

Thanks

Andy W

[Mike Harrison]

To increase available HW pressure/flow ?

[Lurch]

On Mon, 28 Jun 2004 13:11:09 GMT, [e-mail] (Andy W) strung together this:

It sounds like a gravity system with an indirect tank. I assume there are no other valves in the a\c. The pump pumps hot water from the boiler through the radiators and also through a coil in the tank to heat the water up, although a gravity system usually has the pump by the boiler but you never know!

[Andy W]

No it's pumping into the tank itself, not the coil.

There is a CH pump near the boiler but this is not relevant here.

Andy

[ski]

It could be a secoundary circulation pump. In some large houses it would pump water hot around in a circuit and back to the cylinder so that whenever someone opens a hot tap the hot water is available almost instantly

[John Stumbles]

But then it would pump back into somewhere near the top of the cylinder, not somewhere near the bottom.

I'm inclined to agree with Mike Harrison that it might boost the hot water pressure & flow. Is that what seems to be happening when it's running? Is the water it pumps hot or cold (i.e. are the pipes hot or cold)? And is there any sign of a flow switch to turn it on when there's any flow to boost?

[mike ring]

"ski" wrote in news:cbpo28$3n1$ [e-mail]:

If this is true the hot taps would have to be bypassed by some means to allow a small flow when closed. (or have I got it wrong)

Perhaps Andy could check on this.

mike

[Lurch]

On Mon, 28 Jun 2004 14:45:24 GMT, [e-mail] (Andy W) strung together this:

That's me stumped then!

[nick smith]

Having read the whole thread on this I can only think its an attempt to slightly pressurise the DHW cylinder - a bit amateurish and a bit of a risk, but perhaps it was done by someone who tested that the pump was only capable of a few psi max static pressure and less when water flowing, which was assessed to be within the capabilities of the system as regards "static head plus static pump pressure" . Perhaps to provide a better shower, but I would have thought cold should have been "pumped" too to avoid imbalance. I also wonder if it "pumped over" into the cold tank. Nick

[Andy W]

pressure

I think you are right, it does seem to pump only cold, so not a HW ring main. A pumped shower has been installed at a later date so this might be why the pump in question seems not to have been used for a while (hence seized). I think I'll probably just leave it switched off.

Andy