DIY Doctor

central heating pump renewal ???

Postby miklos » Fri Nov 09, 2007 12:26 pm

Hi- for some time now one of my central heating radiators has been very slow to reach operating temp. I had cause to turn off one of my upstairs rads at the thermostat recently. Since then after turning thermostat back on full,I have not been able to get any heat at all into this rad . I have bled all the rads in the house until water runs from each but it has not made any difference. Could it be that my pump is not working as it should? it is extemely hot to touch when running. Is this normal? Is there any check that I can make before purchasing a new pump which I may not need.My pump model is GRUNDFUS SELECTRIC ups 15-50. Any help would be much appreciated.
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Postby htg engineer » Fri Nov 09, 2007 3:52 pm

The pump will have a switch on the head marked I, II & III, these are the speed settings try turning up to III.

Also try venting the pump - turn the big silver screw anti-clockwise. There should be water there. If it's steam that comes out, then the pump is faulty and overheating.

Pretty easy to change the pump, as long as the pump valves don't leak (probably will) as you look at the pump there's 4 bolts securing the head to the body undo these and put the new head on the same way. Ensure the rubber seal is in place.
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Postby holland park heating » Fri Nov 09, 2007 7:35 pm

gently tap the side of the TRV.somtimes the internal pin gets stuck.
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Postby roger196 » Fri Nov 09, 2007 8:05 pm

If all the other rads are working ok, then the problem is an airlock in the pipes to the cold rad. try turning off all the other rads to force water thru this rad only. The turning off process should be done slowly by turning the TRV's down to zero on first one rad and then the next and so on. Check the cold rad at each stage.
Have you bled your ch pump ( a lack of water inside often makes them run hot). Isolate boiler electrics by removing fuse before bleeding.
There is an arrow on the ch pump which tells you the direction of water flow. If the pump is situated outside the boiler , you can grasp the outflow pipe about ten inches from the pump which will tell you if water is flowing. If the pump is within the boiler, a hand on the flow pipe (immediately below the boiler) compared to the return gives the same info. Take great care when doing this if access is restricted as there are a lot of very hot surfaces around not to mention electric cables.
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