When is a pump happiest?

[PaulAH]

Nice and simple: How do you determine the best setting for a Grundfos... 1, 2 or 3?

 

[kevplumb]

the best setting is the lowest that will heat the system without undue noise assuming its correctly balanced

 

[PaulAH]

Thanks, Kev. Please expand

the best setting is the lowest that will heat the system

The system will "heat" whatever the setting

without undue noise

There is no undue noise at any setting

assuming its correctly balanced

And how do you achieve that? Flow /return temp difference?

 

[masona]

The system will "heat" whatever the setting

True, but slower the flow, the quicker it will heat up in the boiler casing.

 

[oilman]

Setting is to get temperature difference on flow and return pipes nearest to 11 deg C once the system is hot and in "steady" state.

Heat transfer from flame to water will be fastest when water is coldest.

 

[PaulAH]

I'm confused. The temperature difference is determined partly by the amount each rad is stopped down and partly by the speed of the pump. Which came first?

And isn't this is all a compromise? An ideal setting with all zones open would, presumably, be far from ideal when there's HW demand only - the water will be flying around like Scalextric. Unless you want to stand there day & night with your hand on the speed controller...