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Issue with mid-position valve

Discussion in 'Plumbing and Central Heating' started by Hallucyn8, 3 Jan 2021.

  1. Hallucyn8

    Hallucyn8

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    First the caveat that I've searched the forum and couldn't find my specific question answered so if I've missed it somewhere I apologise in advance :)

    A week or so ago the other half commented that the hot water was hotter than usual so knowing that we have a V4073A mid-position valve fitted and having a general knowledge of how it's meant to work I went to check the pipes in the airing cupboard. Despite the hot water only coming on for a hour in the morning and an hour in the evening on the programmer (and having been off for several hours) the pipe to the hot water tank was still hot (central heating was either running or had been recently running at this point).

    I've had the powerhead fail on me previously (and I had replaced it myself as it's a new style head that can be replaced without draining down the system). So I did some tests with cycling the hot water and central heating on a off and heard the motor making a "ticking" noise specifically while it was being held in the mid-position. A quick Google suggested the powerhead was failing or had failed so as it was between Christmas and new year and I didn't fancy calling out a plumber, and as replacing the powerhead is a relatively quick and inexpensive option, I ordered a new one. I didn't do any tests with manually moving the valve position as the ticking of the powerhead had, I thought, told me all I needed to know.

    I've fitted the new powerhead today expecting everything to be back to normal but failed on the checkout tests. Basically both hot water and central heating pipes are still both getting hot even when only the hot water or only the central heating is on. I can hear the motor moving when cycling between only hot water, only central heating and both at the same time and it is no longer ticking.

    I've pretty much resigned myself to calling out a plumber now but I have noticed after setting the programmer and thermostats back to normal settings that after the central heating has been running for half an hour or so the pipe from the boiler to the mid-position valve and the pipe from the valve to the radiators is hot to the point I can only leave my had on for about a second but the pipe to the hot water is not getting as hot but is hot enough that it must still be getting some of the flow.

    So to cut to the chase is it likely to be the valve itself failing and not completely blocking off the hot water pipe when only the central heating is on (and presumably vice versa)? Is there anything else I can do or test before I call a plumber?
     
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  3. stem

    stem

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    The hot water port only is normally open when the valve is not powered. When hot water and heating are required, the white wire becomes live and the valve moves to the mid position, then when the hot water goes off the grey wire becomes live and the valve winds fully across to close off the hot water port.

    Usually the fault you describe, assuming the valve is working correctly is due to the grey wire not becoming live and closing the hot water port. The grey wire is connected to the 'Hot Water off' signal from the programmer and the 'Hot Water satisfied' terminal of the cylinder thermostat. If the grey wire doesn't get a live from these connections, the hot water port won't close, and the hot water will be heated whenever the boiler is running.

    [​IMG]
     
  4. oldbuffer

    oldbuffer

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    1. You could remove the actuator and turn the spindle by hand to see if it is sealing. They only move about 20 degrees from water to mid to heating.
    2. You can get the "wet" bits for that Honeywell valve separately, so if you have just bought a new actuator, you might consider just buying the valve part and re-using the new head.
     
  5. DIYnot Local

    DIYnot Local

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