Should the spindle of a water pump be immovable and static?

25 May 2023
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United Kingdom
Hello everyone, I'm hoping you can give me some guidance on a long going issue with my boiler. It is an 18 year old Glow worm 24 ci.

About 3 weeks ago my boiler decided to fart up and stopped working, called the gas engineer, diagnosed the issue, PCB was faulty. Quoted £350 for a replacement and £84 for a 5 minute visual check, fair enough. Ordered PCB advance replacement on ebay for £40.

Call the engineer again to for the PCB on emergency charge of £144 to fix it ASAP as boiler had broken down 3 days before my planned trip abroad LOVELY! Fitted new PCB, great, now I'll have hot water again, new problem water pump doesn't work. Engineer reckons the faulty PCB might have fried the water pump.

To keep a very long story short, ordered and fit in some other parts, including filling loop, water pressure sensor, and 1st replacement waterpump, some mismatches as the exact parts are hard to come by, lots of money spent, mostly on labour. Ordered a used groundofs UP 15 50 A0 from ebay. Seller gurantees it is working, electrical tested and checked. Fast forward to today. Water pump arrives, very creeky and leaves to be desired. WD40 will save the day, got it spinning properly when hand spun.

Ordered used water pump from ebay, my concern and problem is that the spindle on the back is loose in the up and down direction. If I force it open it will come out revealing the interior of the pump and the magnets. Now all the other pumps that I've seen (not that many to be fair) have a solid spindle that can't be opened even if forced. Released the water in the system, fit the pump in, fill the system back up to 1 bar. circulate the water to release any trapped air. Now when I turn on the hot tap water pressure builds back up very quickly (5 sec from 1.1 bar to 2.5). So i immediately turn off the boiler. I feel like I'm at a loss. If I'd know it would be such a nightmare to fix an old but good condition boiler I would've just bought an installed a new one.

Any advice is welcome and thank you for reading so far.
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1st lesson I guess is never by 2nd hand CH items, especially ones that were immersed in water and then left and have probably reached the end of their life anyway, unless they are recon'd with a guarantee. When it gets into hundreds of pounds of costs though, then I always ask the client is it worth it.

As far as the pressure rise is concerned then that could be a circulation issue or an expansion vessel issue. Hard to say not being onsite. Both F&R valves open properly?

P.s. Exact replacement parts aren't that hard to come by - if they are bought new - can be expensive though.

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