Thinking of implementing proportional pump control to raise efficiency in our hot water based heating system.

Proper proportional control is possible using PWM control in high quality pumps like the Grundfos Alpha series or some Wilo pumps. They have elaborate, 2 way communication for very accurate control - however they do have a price premium. Especially, if one already is in possession of simpler pumps...

However, is it possible to do something similar using the "basic" ones, like these below, having 3 levels of speed available?

They have 3 levels of speed available, so control is definitely possible, but as I'm not familiar with the internals, difficult to tell how that works.

Ideas I had for speed control:

  • TRIAC based phase control ("dimmer")
  • PWM chopping of AC voltage
  • Hypothetical: AC voltage level control

Is any of these possible to do with these simple (and very very inexpensive) pumps? Of course none of these implementations would have the two way communication and error reporting part, but still, at least control would be possible...

Image of "simple" pump - IBO OHI 3 level speed control pump

Specification of IBO OHI pumps

  • 1
    It appears that this pump has a mechanical switch. Your question, if I understand correctly, is to be able to replace the mechanical switch with some sort of electronically controlled switch. Is this possible? I'm sure it is. Can you do it? Who knows. Will it void the warranty? I'd suggest that's a certainty. Are you certain that the pump(s) is the lowest hanging fruit in improving the efficiency of your heating system? There may be bigger bang-for-buck things you could pursue that won't impact warranties of somewhat critical components.
    – FreeMan
    Commented Jan 13, 2023 at 12:47
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    Also, your experimenting to figure out how to control this electronically may end up destroying more $ pumps than it would to simply buy a $$$ pump designed for this in the first place.
    – FreeMan
    Commented Jan 13, 2023 at 12:47
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    I believe the typical approach with fixed-speed pumps is to use a mixing valve to set the water temperature (pumping the same amount of water, but mixing in just enough hot water to hit the target temperature) Whether that costs more than the fancier pump is up to your shopping and system design skills. Almost always the boring stuff (air-seal and insulate) will be better bang for the buck.
    – Ecnerwal
    Commented Jan 13, 2023 at 14:39
  • @FreeMan this is why I ask :) I don't want to experiment firsthand - if someone has a way already, that's good. As these pumps don't really have a resale value, I was looking for a low cost way to improve on the current setup to save some electricity while having the same level of service. I was looking at external ways, i.e. putting an Arduino controlled dimmer circuit in front of the pump or similar - tinkering on the internals of the pumps seem to be a tad too intrusive for me.
    – ppeterka
    Commented Jan 13, 2023 at 17:24
  • @Ecnerwal yep, the "boring stuff" is also being implemented, this part is currently only being researched in theoretical basis, but when I touch something I like to explore a bit beyond what's considered normal and reasonable...
    – ppeterka
    Commented Jan 13, 2023 at 17:54

2 Answers 2


There are quite a lot of these modern controllable variable-speed circulators available on the used market. I bought a few and saved quite a lot of money, so you might want to try that.

They're asynchronous motors and the speed control works pretty much like a 3-speed fan.

The controllable ones simply include a small low-power VFD, so if you want fine speed control, you can get a cheap VFD. It remains to be seen whether that will cost more than a full-featured pump, though.

These motors usually don't like non-sinusoid waveforms. If you use a triac, it's probably going to vibrate at 100Hz or make weird noises.


In theory, a common way that buildings would control a similar system is with a Variable Frequency Drive (VFD).

Basically, you just have a drive between the power source and the motor that reduces the frequency, to reduce the load when there is less demand. In new commercial construction, you see this all the time for the large pumps and fan motors in the building.

To me, it seems like it would be easier to make this work than your potential solutions, if a compatible VFD is a common drive you can buy. All that said, I'm no expert on the electrical side, and I dont know if it would be possible to find a drive that works properly and safely with this specific pump. I also suspect it could be at least as expensive as the pump itself for this size pump.

I was on the fence between this being a comment or an answer, so it might not be super helpful, but its definitely another avenue you could explore.

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