Radiator getting hot when Hot Water on

Discussion in 'Plumbing and Central Heating' started by scooby52, 15 Jul 2018.

  1. scooby52

    scooby52

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    Hi folks,

    Quite a common problem, now we are in summer and the Central Heating has been turned off at the programmer, I found a radiator getting hot, when the boiler was responding to demand for Hot Water. However, I have not been able to determine the component causing the problem, and am looking for some assistance.

    I have a Honeywell V4073A valve, and as predicted, when the Hot Water tank is calling for hot water, and the boiler and pump are working, hot water is also going via port B [correction, port A - thanks to Ianmcd] to the CH as the CH pipe gets hot. I assume this is either the valve not in the right position, perhaps in the mid position, or the ball inside the valve has worn. So I need to work out if it's just the Actuator/power head that needs replacing, or the valve body (or even just the ball inside the valve).

    The wiring seems correct, and the white/grey wires are live when expected for the 3 options of HW, HW+CH and CH only. But when the power is switched off at the Fused spur, and there is nothing live in the wiring box by the valve/pump/hot water tank, and I move the lever in the powerhead, it moves freely with no resistance at all. I have read lots of pages that say there should be resistance when power is off, but I cannot determine the significance of this?

    With the lid off the powerhead, I can see movement when changing from Hot Water, to HW + CH, to CH only, so it appears the powerhead is moving the valve. Maybe it's the ball inside the valve that has become worn, and is letting water through into the CH circuit?

    If I remove the powerhead completely, with the power off, and move the lever, then there is resistance so the springs are working. So why is there no resistance when it is attached to the valve and has no power? This suggests one of the wires is energised, so I checked the 5 wires going to the valve and none were live. Another test I did was with powerhead removed, I turned the power on, and changed the programmes, and could see and hear movement, although it was quite clunky, and jumped a lot.

    When the powerhead was removed, I tried to rotate the spindle in the valve, and it was too stiff for fingers, but moved with pliers.

    So, what do you reckon? Is it the actuator/powerhead that is the problem, or the valve? I am happy to buy a new powerhead and fit myself (although not cheap), but would probably get a plumber in for replacing the valve, as it does not have convenient isolation valves, or some that were too stiff for me.

    Thanks in advance.

    Ian
     
    Last edited: 15 Jul 2018
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  3. Crofton Gas

    Crofton Gas

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    With the head removed turn on hot water and manually turn the spindle if heat still goes down the CH side then the three port needs replacing.
     
  4. ianmcd

    ianmcd

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    Port B is the HW port, port A is the heating port
     
  5. scooby52

    scooby52

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    @Crofton Gas - Thanks! I will try that
    @ianmcd - D'oh, apologies. I keep thinking HW is A as it's the default (open when no power). I will correct my post
     
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  7. SwitchTheElectricsOff

    SwitchTheElectricsOff

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    Hi Ian

    I had exactly the same issue a few months back with my inlaws system, it turned out that the little bit of rubber in the valve became too hard to turn and got stuck half way, in the end I replaced the lot with a Drayton actuator, works really well. Draining down the system and doing the work took about an hour and a half (never done it before). It's really easy to change too, just needed some confidence (y)

     
  8. 75pete

    75pete

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    Expect after the reading you have been doing about the valve, you will know that if the valve has a bump in its top lid, it makes it more serviceable.
     
  9. scooby52

    scooby52

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    A quick update. I decided to try changing the ball in the valve first, as it's much cheaper and easier than replacing the whole valve, but this didn't solve the problem. So I bought a new Honeywell V4073A (from ebay) and fitted it. For swapping the ball, and fitting the new valve, I used bungs in the F/E tank to create a vacuum, which worked well both times, and avoided the hassle of draining and refilling the system. New valve working nicely.

    I have read many posts from plumbers who suggest bungs are not for the faint-hearted (or DIY'ers), and I did buy some 22mm stop ends in case it went wrong and I needed to block the pipes and call in a pro, but it all went well for me.
    Thanks for your tips, and although I did have to replace the whole valve in the end, at least I had proved it was the problem, rather than just assuming it was.
     
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  10. SwitchTheElectricsOff

    SwitchTheElectricsOff

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    Glad it all worked out!

     
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