Multi-speed pump - how does it work?

[Kimalin]

I have a Grundfos UPE 25-25 (180) attached to my heating system. It is a 3-speed pump (as indicated by different Morse code patterns on a LED) but has no manual speed selector switch. When I apply 230v directly to it, it runs at the minimum speed. My main question is- how does the boiler tell the pump which speed to run at. Is it to do with voltage? Second question - can I replace this with a simple one-speed pump (connected to mains) and what would be a good one to get? (Fittings are 1.5”). The existing model isn’t made any more anyway. Many thanks.

 

[townfanjon]

The boiler doesnt tell the pump what speed to run at your pumps is automatic it selects its own speed .
Single speed pumps , havent seen one in years , mostly 3 speed but even those are “ rocking horse” these days .