Central heating pump repair

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How I repaired a failed central heating pump.

Symptoms: scraping noises, varying speed, boiler overheating & cutting out rapidly, and ultimately it seized.

The large central plug was undone with a screwdriver to gain access to the end of the pump shaft. A screwdriver in the shaft's slot managed to get it to move again. The pump was run for a minute after replacing the plug, it did not sound well. The plug was then removed and let drip for a minute to flush any loosened muck out of the space round the shaft. With plug refitted it now ran quietly & consistently, but still wasn't moving much water.

Now to tackle the impellor problem. With a large screwdriver and a good bit of force the valves either side of the pump were turned off. These valves are typically found to be jammed.

The pump body is in 2 sections bolted together. The bolts were undone and much mallety persuasion used to separate the pump halves. The rotor/impellor was a hollow design and 100% jammed full of corrosion products & fragments of metal. No wonder it didn't work! A jeweller's screwdriver worked better than a bit of wire to slowly unblock the impellor - the muck was very firmly wedged and took 10-15 minutes to gradually remove.

I had little faith that the rubber ring would reseal and had no replacement to hand. So I smeared a very little diluted linseed putty round the rubber ring & reassembled.

Job done! 20 minutes or so work saved fitting a new pump. It's been fine since.