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Discuss Modulating Condensing Bolier - what style pump is recommended ? in the Central Heating Forum area at

  1. Bert bassett

    Bert bassett New Member


    My second post :)

    Recently I had a Vaillent 418 ecofit pure open vent boiler installed onto an old system ( the installers were rubbish, over promised and under delivered)

    I am now looking at getting the best efficiency out of the system and the boiler by getting the return temp below 55 degrees

    So i plan to remove the straight through (flow to return) bypass from the last radiator and replace the TRV on that rad with open lockshield valves (is that a good idea ?)

    The existing pump is 24 years old, so i am looking at a new pump, i thought it would be straight forwards to get a pump that provided a constant flow (so that the boiler does not cycle as TRV's come in and out).

    Maybe i do not understand fully the difference of the Grundfos Alpha 2L (constant pressure and proportional pressure)... do any of these create a constant flowrate ?

    Are they recommended for a modulating condensing boiler ?

    Any advice will be appreciated

    Many Thanks
  2. king of pipes

    king of pipes Trusted Plumber GSR

    Dab Evosta gives you the option, any pictures of this install you can go fully trv but you should ensure you have a auto bypass fitted at least 1.5m away from the boiler i cant believe a installer would have left a 24year old pump in on a upgrade ? Good practice is change the pump and valves fit a mag filter , all controls , the programmer , and at least the radiator valves , a chemical clean with a hot flush ,then cold flush . cheers kop

    • Like Like x 1
  3. Bert bassett

    Bert bassett New Member

    Hello Thanks for the reply,

    I have looked at so many of those diagrams i am now going mad... my reason for coming to the forum as i am sure i do not understand them correctly.

    The reason i am thinking of removing the bypass across this rad is that this is a curved bay window rad about 2.5m long, i cannot get one side very warm.... all of the heat goes through the bypass.
    This rad is the only source of heat in the living room, and i want the most heat out of it.

    If i try to balance the other rads to increase the flow through it.. the boiler starts to short cycle.

    PS, a new Nest room thermostat controller was installed, along with an ecomag filter.
    The filter is on the boiler flow, the wrong place I am sure.. I have contacted the manufacturer for the filter and they have sent diagrams showing it can go anywhere... so i cannot take that back to the installer.

    The system was power mag flushed, but i think all of the pressure went through the bypass.... i have since removed the bay window rad and flushed it with a hose.. the amount of black sludge was unbelievable.
  4. Bert bassett

    Bert bassett New Member

    a pic of the system

    Heating Pic.jpg
  5. jtsplumbing

    jtsplumbing Plumber GSR

    Bit of a mess, is the cover from the diverter valve missing ? you also have a old style bypass just below the pump.
  6. Bert bassett

    Bert bassett New Member

    big mess.. i was hoping it was all going to be improved.. the cover for the valve is under there somewhere :)
  7. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Did they charge you a fortune?
  8. Bert bassett

    Bert bassett New Member

    Guess so, not really sure.... the old boiler and heating ran for 24 years without anything ever being done to it... so trying to be a little bit more modern ...this came with 10 years warranty and service included.. so i figure if the company stays afloat i should have 10 years more of trouble free heating (as if !!!)
    • Funny Funny x 1
  9. bogrodder

    bogrodder GSR

    Is that magnetic filter is on the boiler flow, if so it’s a big no no, as it’s an obstruction to the open vent if the filter valves are closed.
  10. Bert bassett

    Bert bassett New Member

    Yes it is on the flow.... all i could find says it is not to go there.. but the filter manufacturer sent me the pic below

  11. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Pic not working
  12. Bert bassett

    Bert bassett New Member

    from the filter manufacturer

    Eco mag position.png
  13. bogrodder

    bogrodder GSR

    What’s the make and model of this filter please?
  14. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    That diagram does not surprise me. You can fit a magna clean on the flow if there is nowhere else to put it.
  15. jtsplumbing

    jtsplumbing Plumber GSR

    Can you do a photo of boiler & pipes, filter is always best on return, idea being its stops rubbish getting back to boiler, but on odd occasions you have to fit it on the flow, maybe position or accessibility of pipe work
    • Agree Agree x 1
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