Then I would just measure the current, it either goes above a preset level at or inside a given period of time or it doesn't. This feeds a device along the lines of a watchdog timer or often called a "missing pulse detector". When that happens you latch an alarm which can be audible, visual or both. This does not need to be complicated and it can be as simple or complex as you want or need. You can also either build circuit(s) or just put together a few over the counter turn key modules. You have a 24 VDC pump which either draws current (running) or doesn't, not running. Forget the term power since it's 24 VDC I would just look for current. You mention 100 watts so at 24 volts 100 watts is just over 4 amps so set a 2 amp threshold. Above 2 amps you get a pulse for whatever duration the pump runs. If you do not get a pulse within 10 min (or whatever you want) you get an alarm which requires a manual reset.
Ron
Ron
