cross-posted from: https://lemmy.dbzer0.com/post/26703241

This diagram is from the service manual of a combi boiler. It’s a flow sensor which detects whether hot water is running, which is then used to trigger on-demand heat and switch a diverter to take radiators out of the loop.

In English, the diagram shows:

  • X ⅔ red wire (+5V)
  • X 2/2 black wire (ground)
  • X 2/6 green wire (signal)

I need to know what those fractions mean. I took the voltage measurements in this video:

I cannot necessarily trust the model in that video to have the same specs as mine. My voltmeter detected 4.68 V on the red input wire showing that the sensor is well fed. The green “signal” wire is supposed to be 0 V at rest and 2 V with water running (or I think the reverse of that is used in some models). In my case the green wire is ~1.33 V at rest and ~0.66 V when water is running. I need to know if these readings are normal as I troubleshoot this problem.

update

@[email protected] and a couple others gave the answer I was after. Then @[email protected] helped solve the underlying problem. The theory that the sensor was fine but the board was not drove me to test the sensor in isolation. The sensor gave correct output in isolation. Then I connected it back to the motherboard to retest and reconfirm that it’s still broken. But it actually worked. The hot water suddenly and mysteriously works now. I guess the act of draining the water and unplugging the connector then reconnecting and repressurizing caused it to work. It may be temporary, since in the past it was hit or miss whether it would work.