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 purpose of this was to grind up the muck slowing it down. 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 hollow rotor/impellor was 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.