Central Heating Pump Question

I have an indirect, vented heating system. The circulation pump needs replacing (about 10 yrs old and bearings are noisy).

The existing pump has obviously been working fine for years. It is a Grundfos 15/50. My inclination is to fit the exact same one.

Question: I see from the specification for all the main domestic pumps (including Grundfos) that the max. head height is 5-6m. Only the light industrial pumps are more than this.

The pump is installed next to the boiler in the basement and the highest radiator is about 12m above. Unless I'm missing something the old pump shouldn't have worked and the property ideally needs a heavier duty pump? Having said that I see that my nieghbours identical property has the same pump - and theirs is working fine too.

Am I mis-interpreting the spec or is the spec conservative and in practise they work well above the maximum head specified?

Thanks,

Justin Leese, UK

It's a closed system. Water coming down weighs the same as water going up. (a bit more in fact)

A 15-50 would be fine to about 70,000Btu/hr I think it works out.
10 years isn't long for a Grundfos. Make sure the motor shaft is horizontal. Dirty systems wear them out too.

ChrisR said:

It's a closed system. Water coming down weighs the same as water going up. (a bit more in fact)

A 15-50 would be fine to about 70,000Btu/hr I think it works out.
10 years isn't long for a Grundfos. Make sure the motor shaft is horizontal. Dirty systems wear them out too.

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Mines 25 year old this year

And they dont have bearings so if it noisy then its probably sludge etc

Closed system - flow and return at approx same weight (return slightly heavier because colder and denser). Hence relative head is low. Makes sense. Thanks. Wondered how those radiators on the 4th floor still managed to get hot!

Yes - you are spot on, uncoupled the old pump and it was full of sludge. Just about to flush the system a few times then re-fill with fresh water and fernox.

Regards,

Justin

....And they dont have bearings ........

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So what supports the rotating part?