Heating advice - Heating only comes on when hot water on

Discussion in 'Plumbers' Talk' started by ldnguy, Mar 1, 2015.

  1. ldnguy

    ldnguy New Member

    Hello,
    Some advice please - trying to diagnose a heating issue.

    Set-up
    • Standard Vaillant 418 boiler
    • Vented hot water cylinder in airing cupboard
    • 3 port mid point valve in airing cupboard
    • Grundfos pump in airing cupboard
    Issue
    • Every so often (becoming more frequent) when the programmer kicks in for heating only, the rads don't heat up until you also turn on the hot water at programmer.
    Troubleshooting
    This morning before the programmer had turned on for the day (everything in system was cool), I tried some tests, by manually triggering the programmer. Because the Honeywell 3 port valve doesn't have any indicators, I checked result by feeling pipe work after 5 minutes.

    HW off / CH on - result is no rads heating up (Grundfos pump NOT on)
    HW on / CH on - result is rads heating up (Grundfos pump on)
    HW on / CH off - result is no rads heating up
    HW off / CH off - result is no rads heating up

    Then later tried again, different result:
    HW on / CH on - result is rads heating up
    HW off / CH on - result is rads heating up


    I'm a bit confused, but think this generally points to a sticking Honeywell 3 port valve (like this one).
    Do you guys agree? Any tips to troubleshoot further?

    [​IMG]
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    3 port valve needs replacing
     
    ldnguy likes this.
  3. ldnguy

    ldnguy New Member

    Thanks Dave - would it be expected behaviour that in this situation, the pump is not active?
    HW off / CH on - result is no rads heating up (Grundfos pump NOT on)

    Perhaps is the 3 way valve is stuck closed the pump will not trigger as has nothing to 'pump' or maybe the pumps are flow triggered rather than electrically switched on/off?

    Last question - would you just replace the actuator head or the complete unit inc. brass 3 port connection?
     
    Last edited: Mar 1, 2015
  4. Dave does Gas

    Dave does Gas Screwfix Select

    Change the lot, In my experience just changing the actuator only works in a very few cases as its often the internal workings of the valve that get stiff and cause the actuator to fail.
    You can do the change without draining the system by using a bung kit on the cold feed and open vent in the loft. there will be about a pint or so of water to catch then it should lock up so you can replace the valve
     

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