Over pumping

[blueadarron]

I changed my gravity hot water system to a fully pumped system about 5 years ago. Initially I had a problem with over-pumping, but when I reduced the pump to a lower setting the problem was cured.

I've recently removed a radiator (whilst re-furbing a room) and at the same time flushed the system.

Since then the over pumping has returned and the pump is on its lowest setting.

The pump is in the loft and follows the overflow and then feed by about 50cm.

Is this likely to be a blockage and does anyone have any suggestions on flushing techniques? Or is it the pump, overflow, inlet combination?

 

[seco services]

useally a blockage or bad pipework design.
in your case i would say a blockage.

whats the condition of the water in the f/e ?
whats the condition of the water being pumped over the vent ?

 

[cross thread]

sounds like a badly designed system,check the expansion and cold feed positions

 

[bengasman]

Probably blockage due to flawed design, poor installation and lack of proper maintenance.

 

[blueadarron]

The water in the F/E is clearish with a bit of orange sediment in the bottom. The water in the pumper overflow is clear.

 

[blueadarron]

Any suggestions of the potential problem with the overflow and feed arrangement?

The boiler is in an upstairs room. The outflow goes vertically up into the loft and ends with a t-joint. The overflow is out the top of the t-joint in-line with the vertical up flow from the boiler. The flow to the feed pipe and subsequently the pump comes out of the t-joint at right angles.

Is it the alignment of the overflow directly above the up flow from the boiler the problem?

 

[seco services]

have you a pic etc ?

whats the distance between the vent/feed pipe?

 

[blueadarron]

The attached diagram shows the pipe work layout

Untitled

• blueadarron
• 12 Nov 2009
• 1

 

[seco services]

try running a magnet around the t's on the vent/cold feed area.

 

[blueadarron]

Tried the magnet on the tee's. It doesn't stick. In fact the the over pumping seems to be getting faster.

 

[bengasman]

Pump wrong way round?

 

[heatingman]

what is the measurement of the overflow/vent pipe up and over section? What is the distance from the pump to the base of the expansion tank?

 

[rojaca]

Water level in f+e tank ideally should be 1/3 of head created by pump above the pump (15-50 pump- 5m head/3=1.6m)
Ideally vent pipe better on horizontal section of pipe rather than straight off vertical- something to do with density of water ..mumbo jumbo.. blah blah big burner drivel something something darkside...

 

[heatingman]

its to do with cavitation and the way air bubbles travel in vertical pipe.
Covered it yonks ago at college.
Something like:
Verticaly pumped water swirls and bubbles are in centre of vortex and wizz round fitting, on horizontal pipe bubbles travel along top of water flow.

no doubt someone will come along to contradict or correct me. (It was years ago so digging from grey matter)