noise from pump

16 Mar 2006
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United Kingdom
Hi all, i have a standard CH system using a potterton nettaheat boiler, hot water tank in upstairs linen cupboard and water tanks in loft.we had the circulation pump replaced recently due to the boiler overheat stat cutting out, that all ok now but now we get a load howling scream from the pump occasionally. i turned it down to 2 from 3 but still makes the noise, usually a couple of times a day.the pump is a grunfoss situated next to the hot tank in the airing cupboard. Do you think i have air in the system causing the pump to run dry?

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Try bleeding the pump (with system off). The large screwdriver slot in the head of the pump.
There was a bit of air in the pump but not much. this afternoon the system started up and after 15 mins the pump made the noise ( high pitched whine) and i unscrewed the centre screw a bit, this seemed to stop the noise. now all quiet so far.
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Pump might not be orientated correctly (shaft should be horizontal) or could be sucking in air. Try on lower speed setting and check for suction via vent pipe over CH header tank.

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