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Discuss Central Heating FlowProblems in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Mike Mays

    Mike Mays New Member

    l have a conventional vented fully pumped system from an oil-fired boiler on the ground floor. HW tank is in the 1st floor airing cupboard along with the pump and 3-port valve. 22mm vent pipe rises through the airing cupboard up to the F&E tank in the loft where it rises some 600mm before dropping back to the tank. HW feed tees off the rising vent pipe in the airing cupboard through an air separator then to the pump inlet with the cold feed in between. All was working fine until a recent pump failure. This was duly replaced but then found there was a degree of pumping over even on the pumps lowest speed. It is the correct pump for the installation. Rectified this by re-routing the cold feed into the vent pipe approx. 250mm above the air separator. Cleaned out the air separator and pipework to pump while at it. BUT, now have occasional flow stoppage around the CH circuit? Programmer and 3-port valve/controller all checked OK. Local heating engineer scratching his head as is one of his colleagues who he brought along for a 2nd opinion. Would be very grateful for any suggestions as to where o go from here..
     
  2. Best

    Best Trusted Plumber

    First thoughts on an open system on oil or gas is would it be suitable to have it a sealed system.
     
    • Like Like x 1
  3. John.g

    John.g Active Member

    Any idea what the old pump/model was and its speed setting? and what is the replacement pump/model?.
     
  4. Mike Mays

    Mike Mays New Member

    Nervous about converting to a sealed system as the CH has microbore pipework and is 38 years old. As for the pump, the old one was a fixed speed Wilo, not sure of the model. The new pump is a 3 speed Grundfos UPS2 15-50/60. House has 14 rads but usually only 8 in use now with just 2 of us in the house.
     
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  5. Rob Foster

    Rob Foster Top Contributor!!

    look it worked before, so thats what needs fault finding ...not altering ...aww I will have a look later centralheatking
     
  6. Rob Foster

    Rob Foster Top Contributor!!

    In my opinion as an old very experienced fart ..

    if your system is 38 years old and has been a good friend until this new pump...then on the dont fix what is not broken principle
    I would look very seriously atbthe pump. Who says its ok ?
    its obviously not ! centralheatking
     
  7. Mike Mays

    Mike Mays New Member

    That's a very good point but which pump?
     
  8. John.g

    John.g Active Member

    Re "combined cold feed and vent" that you now have. Originally you had a air separator with 3 pipes?, the inlet at one side, the vent from the top & the outlet to the pump with the cold feed in between the vent & pump?.. Now after this modification, I presume you still have a 3 pipe set up as above, the only difference is now that the cold feed is teed in to the separator vent but the separator outlet pipe is still going to the pump, is this correct?. I am just wondering if the mod is somehow allowing air to be drawn into the pump suction.
    I have a combined cold feed & vent system from first install 42 years ago but no air separator, the cold feed is teed directly into the vent which passes up (and then over) adjacent to the F&E tank.

    The UPS2 was pumping over even at fixed speed 1 so you teed (as above) in the cold feed to the vent, this cured the pump over but you now have a occasional problem with the CH. Did you try fixed speed 2 or even 3 after this.
    Now this suggestion is at odds to what I just said above but you might consider just changing over the pump setting to (proportional pressure) PP 3, this is even a lower setting than the fixed speed 1 but worth a try. You just press and hold the button for > 5 secs to get a flashing green LED and then select PP3 and see how it goes. (page 7 of 16, in attachment).
    Of course as stated above you could have a pump problem, if under warranty, you can get a new one and just change the pump heads. I have a Wilo Yonis Pico 1-6 which is working very well on PP control with 10 rads.
     

    Attached Files:

  9. Rob Foster

    Rob Foster Top Contributor!!

    I work on the complicated is easy and simple is hard principle in my plumbing and heating design business. So keep your new pump it cost plenty I expect, just stick an adjustable valve just beyond it
    like a gate valve and make the pump behave according to what you want and how the old Wilo did ...you can then dick around with the gate to achieve happyness centralheatking
     
    • Informative Informative x 1
  10. Mike Mays

    Mike Mays New Member

     
  11. Mike Mays

    Mike Mays New Member

    Note your suggestion re switching pump to PP3 but was also thinking of cleaning out the pipework again twixt air separator and pump as there's some magnetic activity here. Would it be worth getting rid of the air separator while at it and tee straight into the vent pipe from the pump? You could be right about air being drawn in..
     
  12. Rob Foster

    Rob Foster Top Contributor!!

    yup simplify the whole set up , then you reduce the variable problems ...centralheatking
     
    • Agree Agree x 1
  13. John.g

    John.g Active Member

    Your original pump over problem was probably due to the fact that the UPS2 pump (>6m pump @ speed3 and still a 4M pump @speed1) was more powerful than the one it replaced, speed1 on the ups2 is probably more powerful than speed2 on your old pump).

    However that's history now and you must deal with what you have.
    You "now have occasional flow stoppage around the CH circuit", how was this manifesting itself, was it colder rads or boiler short cycling or tripping on Hi limit stat? or whatever.

    I would first check for any blockages in view of the magnetic activity, also remove the pump and/or pump head and check for blockages in the pump casing ports and in the pump impeller itself. Depending on what you find then you may then decide to get rid of the air separator, I just don't like the idea of the cold feed teeing into the separator vent even though it stopped the pump over.
    As a interim measure if you are happy that the pump isolation valves are holding, why not just remove the pump head and inspect the ports & impeller and flush out from both sides. Dare I say it, ensure that the replacement pump has been installed properly and is pumping in the "right" direction.
     
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  14. Mike Mays

    Mike Mays New Member

    As for the occasional flow stop round the CH circuit, all will be working perfectly well for a few hours then the flow would just stop. I can restart by switching off the CH, switching on the HW circuit then switching the CH back on again - air somewhere around the 3-port valve? Interestingly, there were no CH flow problems when the cold feed was between pump and air separator. After your very helpful comments, now thinking about piping cold back to where it was, get rid of the air separator and then deal with the pump pressure if the pump over returns. On setting one, the pump over was approx. o.5l per min so not a great rate. Could well be sorted by your earlier suggestion of dropping down to one of the PP settings.
     
  15. John.g

    John.g Active Member

    I hope you havn,t got some problem with the 3 port valve, a bit suspicious.
    The UPS2 is a poor choice when using PP control as the three settings are too close together, the max (PP3) setting is 3.0M but in a 6 M pump should really have 4 or 5 settings up to 5.5m to give you the required flow when all systems are open, for example I have my PP setting (Wilo) at 4.0M (up to PP 6.0 M available) to give me that required flow, it then ramps down with the throttling of the TRVs. You may have a low resistance system so why not just change over now to PP3 and see how you get on?, you will soon know if all the rads arn't heating up.
    That pump over of "only" 0.5 LPM will very quickly corrode your system and shouldn't be tolerated under any circumstances.
    I know I'm repeating myself but be happy that the pump is pumping in the right direction first.
     
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