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.
My money is on faulty controller at this point, but I think you’ll need to find someone with electronics chops if you want to avoid just buying parts until it works again.
For what it’s worth, I didn’t mean take the sensor out of the wall, but just electrically unplug it from the controller to see what it does on its own when you turn on the water.
A frequency counter won’t really help you here, I think. You already know to expect ~VCC/2 when water is running, and either VCC or 0V if it isn’t. The speed of the square wave isn’t very relevant.
Yeah I figured that but the terminals on the sensor are hard to reach so I was figuring I would need to remove it. But then it occurred to me that I could leave the thing in place and do the isolated test by unplugging the X2 connector from the motherboard and easily access the pins through that connector. So that’s what I did. Results:
So in isolation the sensor worked correctly. Then I plugged it back into the motherboard and retested to confirm again the bad voltages. But in fact the readings were correct. It’s unclear why it works now. I wonder if the unplugging and replugging of the x2 connector improved a connection that deteriorated somehow.
Thanks for saving me €36! However incidental. If I had not done the test in isolation, I probably would not have messed with the X2 connector. I would have normally just replaced the sensor as an experiment.
(edit) I can hear a ticking sound coming from the motherboard. I’m not sure how long it’s been doing that. It’s quite faint unless I put my ear close to the board. Maybe it’s normal.
Good job troubleshooting.