I know, I’m using the same pump. Maximum coolant temperature is specified at 50°.
1500W with 2x 280 rads will exceed 50° coolant temperature. If you only use it for short(ish) bursts and do not let the coolant reach maximum temperature you might be ok.
Adding a coolant temperature sensor + display (these are available for under 20:money_mouth_face: might be a relatively easy fix, so you can switch off or reduce power when it aproaches critical temps.
The pump is intended for computer Watercooling, where you do not want you water temps above 40° (roughly) because that would defeat the purpose of the Watercooling (lower temps than with air cooling)
Thus they might have gone for a choice of materials which perform nicely up to 50° but could possibly degrade if temps rise much higher.
I do not know the exakt physical reasons, but one idea would be softeners in the sealing surfaces which get dissolved at high temperatures and compromise sealing.
The DDC is safe up to 60C.
The fluid temp probably won’t reach that since not all 1500W are being dissipated as heat, and he can run the fans much faster/louder than a typical PC would have.