3-port valve problem V4073A

Discussion in 'Plumbers' Talk' started by Ben__F, May 22, 2024.

  1. Ben__F

    Ben__F New Member

    Main symptom: CH works just fine and is sensitive to the thermostat when HW is off at the programmer. As soon as HW is switched on, rads get hot regardless of room temperature or programmed CH times

    The diverter valve is Honeywell V4073A
    All heating/HW has been off for weeks but the 3 port valve motor was hot (pipes were cold)
    The brass part of the valve does its quarter turn easily
    The motor of the actuator has the correct resistance (2.3kOhm)
    That resistance is only revealed between White and Blue at the junction box end. All other combinations are open.
    It used to work correctly.

    Could this be a problem with the programmer? If it is the valve, do I need a complete valve or just a replacement actuator? Or is it something else?
     
  2. terrymac

    terrymac Screwfix Select

    Sounds like the gate within the valve body is permanently open to both ports. If you set programmer to heating only ,does the hot water cylinder also heat up ?
     
  3. Ben__F

    Ben__F New Member

    No. We normally don't use HW (it's only for when we have guests), so in winter we just have CH only and the water doesn't heat up.
     
  4. If the pipes were cold but valve hot, then I’d say it’s as per terry, valve stuck in mid position
     
  5. terrymac

    terrymac Screwfix Select

    If you don't use hot water ,how do you know the hot water cylinder isn't heating up when only central heating is in use ?
    Could you be mistaken ?
     
    Deleted member 320418 likes this.
  6. Ben__F

    Ben__F New Member

    No, I'm not mistaken about the hot water not heating up when only CH is on. We do use the hot tap sometimes and coldish water comes out.
     
  7. terrymac

    terrymac Screwfix Select

    If you select hot water only,you told us radiators heat up, but does the hot water cylinder heat up too ?
     
  8. Ben__F

    Ben__F New Member

    Yes, sorry - that wasn't clear. Yes, hot water heats up when HW is switched on. The problem is that the CH comes on too whether it is wanted or not. So, CH = always on if the boiler is running. HW = On only when HW is required.
     
  9. terrymac

    terrymac Screwfix Select

    Voltages present at various points in the wiring centre would need to be established ,under various settings of the programmer to determine what the fault is, and probably best left to an engineer.
    Fitting a complete new valve is likely to be required ,but testing should be done first to confirm
     
    Deleted member 320418 likes this.
  10. MGW

    MGW Screwfix Select

    I have had radiators getting warm when the micro switch in the three port valve has failed, and some one has latched the valve to bleed position to temporary get around the problem.

    To turn DHW off the three port valve has to travel all the way across, if the CH is running, the valve I seem to remember can be energised for an extended time if the DHW is not used.

    John Ward explains. The three port valve default is DHW so when a boiler needs to cool down there is always some where for the hot water to go, same applies to C Plan, where with the S Plan there is no flow with valves closed, and when a micro switch has failed causing boiler to run when it should not I have seen the pumps fail, theroy there should be a by-pass valve, but in practice often after the pump.

    So there are pros and cons for all the systems and plans, however understanding the Y Plan is hard, this mid-position-valve.jpg diagram of the inside of the valve shows how hard it is to test the valve, you have so many back feeds, likely some V3 micro switch has stuck, but when I had a problem I ended up changing the whole valve mainly as a Sunday and only screwfix was open, so could not buy a head only back then for the make involved, going back some 15 years ago so maybe changed now.
     
    Ben__F likes this.
  11. Ben__F

    Ben__F New Member

    Brilliant, MGW. That video gave me the info I needed to test the actuator and I found that it has mechanical problems: There's so much wobble between the shaft and the cams that the cams don't press the microswitches cleanly. I'm ordering a new actuator.

    I'm still puzzled though! The default (no power) position is HW only and that's what I couldn't get. So, I'm now guessing that the wiring from the programmer is back-to-front (CH/HW) and the actual valve body is back-to-front too. So it worked but in my case, the default position is CH only and it was unable to move all the way to HW only. That's the only way that I can see it makes sense and I'll soon find out if it's right. I'll try to remember to post the final conclusion on here when it's done.
     
    Last edited: May 25, 2024
  12. Ben__F

    Ben__F New Member

    It's done and working. It wasn't the wrong way round. The problem was that the springs in the old actuator weren't strong enough to overcome the combined friction in the actuator and valve to turn the valve to the HW only position. It's only a tiny movement from the CH/HW position. The cost of the compatible actuator was £30 so it's cheaper (and drier) than changing the whole valve. Now we can have HW in the summer when we have guests and they will continue to think that we're dead posh.
     
    Deleted member 320418 likes this.
  13. Thanks for the update :)
     

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