CH control upgrade: valve & circulation direction problem.

Discussion in 'UK DIY' started by CliveM, Aug 26, 2004.

  1. CliveM

    CliveM Guest

    Whilst it was warm I decided to add some controls (i.e none before) to the
    central heating system.

    Exiting system is gravity (pumped heating). Two 28mm pipes out of the
    boiler, then a 22mm pumped circuit is taken of the 28mm pipes.

    To keep things simple I went with what I think is called "honeywell C Plan".
    Wiring OK (after a google of this group) but I have a problem.

    Before starting I put heating ok HW only, and checked which was flow &
    return. I then fitted the valve on the return pipe (with the correct flow
    direction A->B) was recommended doing a search and as access was easier.

    After refilling I put HW and CH on, and then noticed that the water was
    trying to flow through the valve (i.e B->A) and that the pump was therefore
    in the return. (i.e when the pump was on, circulation was in the opposite
    direction to what gravity was running before fitting the valve)

    With the HW & CH on the house got warm and all the flow/return pipes by the
    boiler but the HW coil did not heat. Putting the system to HW only also did
    not work. I suspected an airlock somewhere and tried to clear without

    In the end I guessed that I must have been mistaken which pipe was flow &
    return and though that I have fitted the valve in the flow. I then drained
    the system again, and swapped the valve around so that the valve was in the
    flow with direction (A->B). Upon refilling the system, we now had
    HW/HW&CH/CH. When HW only was on, the only the HW feed got hot, then the HW
    return. CH was cold. All seemed ok.

    This morning, put HW only on, and I notice that the water is now flowing in
    the original direction (i.e through the reversed valve B->A) and then up the
    HW feed. There is also now some gravity circulation up the CH feed (but no
    heat in any rad). HW is heating.

    How can the water travel in opposite directions between gravity & pumped. Is
    it possible that gravity flow runs either direction for some reason?

    Most importantly, which way should the valve be fitted, and how can I solve
    this problem?
    CliveM, Aug 26, 2004
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  2. CliveM

    Set Square Guest

    In an earlier contribution to this discussion,
    It sounds like it's the *pump* that you need to turn round, rather than the

    You say that you have ony 2 pipes going to the boiler - 28mm - and that the
    22mm heating circuit branches off these.

    In HW-only mode, gravity flow will be from the top of the boiler and return
    into the bottom. When you turn the pump on, the direction of flow through
    the pump will determine which way the water goes round the CH circuit - all
    the way back to the boiler - including through the bits of 28mm pipe which
    are shared with the HW circuit. Here lies the rub! If your CH flow uses the
    *bottom* connection for flow (which isn't a good idea anyway, because the
    boiler thermostat will be at the top!) and the *top* connection for the
    return, this will interfere with the gravity flow - and either stop it
    altogether or make it go round the "wrong" way.

    So make sure the pump is the right way round. Was your system ok before you
    fitted the valve? Have you touched the pump during your upgrade operation?

    Incidentally, I doubt whether the valve really *cares* which way the water
    goes through it - but you might as well line up the flow with the arrow
    while you're at it. [Unless anyone knows different?]
    Set Square, Aug 26, 2004
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  3. CliveM

    CliveM Guest

    Most importantly, which way should the valve be fitted, and how can I
    Been thinking about this untill I got a reply, and came to the conclusion
    that the pump should be reversed to that all the water goes in the same
    direction. Was a bit worried about reversing the pumped from in case it
    affected any of the TRV.

    Yep, thats right.
    Think you are right. When the HW is on (i.e gravity) water heats ok. When CH
    is on heating is OK. When HW and CH are together we get no hotwater.
    System worked ok before, either HW only or HW & CH. Pump not touched only
    the valve put in place which seems to have affected flow.
    CliveM, Aug 26, 2004
  4. CliveM

    Set Square Guest

    In an earlier contribution to this discussion,
    Seems very odd. Maybe the HW circuit has *always* flowed the other way when
    the pump is on, and maybe it doesn't matter.

    Have you wired the valve *exactly* as per the C-Plan diagram in ?

    The only effect of the valve (provided it is open!) should be to put a
    little bit of extra restriction into the HW circuit - but not enough to
    matter. [It *is* a 28mm valve, isn't it?] Have you checked that, when you
    are not getting hot water, the valve is actually *open* and that the boiler
    is still running for the CH? I'm trying to think of how you could have
    mis-wired it to make the valve close when the CH is on, but I can't
    instantly see how to do this. Anyway, it worth double-checking the wiring -
    and maybe getting someone else to check it too.
    Set Square, Aug 26, 2004
  5. CliveM

    CliveM Guest

    System worked ok before, either HW only or HW & CH. Pump not touched
    Spent more time trying to work out what is happening, then fitting the
    control in the first place! - never mind good excercise up the ladder.
    Yep, definatly a 28mm fitting - the bore through the valve is a bit smaller
    but shouldnt be a problem as the system gives HW only which is just gravity
    Wiring OK. If HW only, the valve opens, boiler fires, pump off. If CH only,
    valve closed boiler fires, pump runs, if HW&CH then Pump runs, valve open
    boiler fires. - If the valve is open and boiler on there should be HW.
    I think you may have got its- its always flowed the other way round and no
    one noticed, even though it is a bit odd. The gravity circuit runs the
    oposite way round depending if pump is on or gravity only.

    From what I can make out (and I think I understand it now) through the maze
    of plumbing, what happens is a follows.

    When the pump is running, the CH return pumps from its 22mm into a T to the
    28mm which then goes (Boiler Return ^ HW). This is resulting in 1/2 the CH
    return being pumped to the boiler, and 1/2 to the HW (which then becomes the
    Flow). When the HW pipes return it arrives at the 28mm T with the 22mm CH
    Flow comming off. As the HW return cant move the against the pumped CH flow,
    what happens is that the HW return water get "sucked off" the T piece by the
    pump (i.e CH FLOW ^ HW RETURN) so CH flow is a combination of Boiler Flow
    and the HW return. (or to make it simple, CH returned water is pumped as HW
    flow, and HW return if then pump round the CH circuit as CH flow)

    This then results in HW being passed through the cylinder from the bottom up
    but is obviously pumped when pump is on.

    And you wonder why I am confused about all this. Anyway this now seems to
    have resulted in that we do get HW when CH on (and it must have always been
    like this), but that I have just been confused over the last 3 days! I
    suspect that there was a load of air in the system which caused the initial
    problem. (you could hear it in the pump, and boiler cut out a couple of
    times), which now seems to have cleared.

    Time to put the tools away (I hope) - thanks for all your help.
    CliveM, Aug 27, 2004
  6. CliveM

    Set Square Guest

    In an earlier contribution to this discussion,
    Are you saying that it's now working ok?

    Its not a very good idea sending "spent" CH water round the HW circuit,
    because it will already have cooled a bit, so HW recovery will be slow. At
    the point where the return flow from the CH rejoins (what is supposed to be)
    the return flow from the HW, it might be an idea to use a sweep tee rather
    than an ordinary one. If fitted with the sweep in the right direction it
    would be far harder for the water to go the wrong way.

    How near the boiler is the point where the circuits split? Does your boiler
    have 4 connection points, two of which are currently blanked off? If so, and
    if the split is fairly near the boiler, you could consider having two
    totally independent circuits all the way back to the boiler with no shared
    pipework. That should definitely fix the problem.

    Alternatively, you could convert to a fully pumped S-Plan system. You would
    need an additional, zone valve, and you would have to move the pump into the
    shared bit of pipework.
    Set Square, Aug 27, 2004
  7. CliveM

    CliveM Guest

    Are you saying that it's now working ok?

    No boiler has 2 connections.

    As it is working now (i.e there is hot water) - I will leave it as is for a
    week or too - and then replumb the system.
    CliveM, Aug 27, 2004
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