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Hello, I can help you with this.Normally, I would say that the MZV actuator is faulty, but that's less likely since yours is fairly new. Did the problem start as soon as you had the new actuator, or before?
I'm online, but this isn't quite like an interactive chat, so there will be natural gaps in our exchanges. But rest assured I will see your replies and will respond.
Assuming for now that the new actuator has no fault, then the fault is likely to be in the wiring to it, or of the system. It might have predated the change in valve/actuator, but of course the installer should have fully tested it. I guess you're finding out much later that there's a fault, and can't be sure that they tested it?
I don't mean that it might be incompatible, no. There are no compatibility issues of that nature.When the actuator is replaced it involves re-making connections at the wiring centre. If the previous actuator was a different make, then it increases the chances of making a mistake in those connections. Or, a mistake could have been made long ago, and the wiring could always have been wrong, and could still be wrong. Or the new actuator could have been faulty out of the box. Or could have become faulty.Before we go too far in any direction, please could you tell me the exact model of the Honeywell actuator? There should be a label on the casing.
OK. If you have the multimeter with you and have time today, I can post here a list of the initial tests you need to do. The first steps will be to turn off the power, remove the wiring centre cover, take a photo (or photos) of all the wiring connections, and then turn on the power and get ready to use the multimeter. You will be testing live connections, so you need to be confident in doing that safely, and sure that there's nothing live that you can accidentally touch, like stray conductor strands.I presume that you're a contractor and you have to visit the property?
OK. Bear with me - I'll post them at lunchtime so you should have them in plenty of time.Depending on the outcome of the tests, we might need some more interaction here, but I suggest taking it one stage at a time.
First of all, some sanity checks.Locate the orange, grey, and white wires from the MZV.1. Power up with no demand on DHW and CH.Verify that there is 240V on grey, and 0V on the other two.2. Create a DHW demand.Verify that there is 240V on the orange, and 0V at the other two.3. Remove the DHW and create a CH demand.Verify that there is 240V at all three of the above.4. Create a DHW demand, and leave the CH demand on.Verify that there is 240V on the orange and white, with 0V on grey._____If any of the above reveals a problem, let me know, and meanwhile identify the cable from the cylinder thermostat - note the terminal numbers and let me know what those numbers are.I'm expecting that tests 1-3 will pass, and test 4 will fail. If this is the case, then you'll need to look for a problem with the connections to the cylinder thermostat.
I meant to ask you to attach a photo of the inside of the wiring centre. That might not be needed, but just in case it is, could you arrange one?