Posting a message to the forum will remove the above advertisement
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss Evosta Circulator Squeeking, Setting Query in the Central Heating Forum area at

  1. Tom723

    Tom723 New Member


    I had a new boiler installed at the beginning of 2018 and the plumber installed a Dab Evosta circulator. A few nights ago it started making a high pitch squeak which can be heard throughout the house. I therefore looked it up and found the instruction manual.

    I tried bleeding the pump but no air came out, only water.

    I did, however, notice that the pump was set to “Constant Differential Pressure” which, according to the manual was for underfloor heating systems. I have radiators.

    When I changed the setting on the pump to “Proportional Differential Pressure” which appears to be for radiators the squeaking stopped!

    My concern is why the plumber initially set it up as Constant as opposed to Proportional? Have I changed anything significant? Is it going to have an adverse affect? Would the initial setting have had an adverse affect over the past year and a quarter?

    I have attached some photos.

    Thank you in advance.



  2. John.g

    John.g Active Member

    IF its like the one in the attachment then it has three constant curves, ("fixed speed"), speed 3 is 7M which is very high if it was set to this, speed 2 is 5.5M which should be more than adequate for most houses.
    It has 6 proportional pressure settings PP6 is the highest at 4.8M (probably the one to go for) and PP5 is 3.8M which may be OK for a 8 rad house or so. The proportional Pressure setting (PP) will mean that the pump speed/head falls with the shutting off of zones or TRVs and saves power.

    Attached Files:

    Last edited: Mar 20, 2019
  3. Chuck

    Chuck Well-Known Member

    If the system works okay with a lower pump setting that's probably a better one to use in many cases.

    It is not uncommon for installers to pay little attention to the details of pump curves and settings, radiator balancing, etc.. I guess that they subscribe to the philosophy that as long as all the radiators get hot the job is done. They also often to leave the settings higher than strictly necessary, 'to be on the safe side'. This is particularly the case when an existing system is being worked on rather than installed from scratch.

    To be honest, I have some sympathy with them. Doing a proper heat loss calculation for each area and then balancing and getting the deltaT values just right for a house takes hours not minutes and needs to be done when the weather is cold, which is not when a planned installation happens. Very few houseowners want to pay the several hundred pounds this sort of commissioning/service cost and it may make relatively little difference in practice anyway.
    • Agree Agree x 1
  4. John.g

    John.g Active Member

    Yes of course, plumbers have to make a few bob as well so will generally set to constant curve (fixed speed 2 or 3). My own (Wilo), I,ve set to PP4 (4M) and it averages around 16W, fixed speed 2 = 25W & fixed speed 3 is 40W so saving assuming ~ 2700 circ pump running hrs/year, 24 kwh/annum, say £5 or, 65 kwh say £12. Of course if XXX million people used the PP setting(s) it would save a power station or two.
    Generally, I would say that you won't get many call backs if you set the pump to a PP setting of 5M or so.
    • Like Like x 1
  5. Tom723

    Tom723 New Member

    Thank you everyone.

    It’s a 4-bed house with 13 radiators and 2 heated towel rails. Do you think the PP6 setting will be sufficient or should I raise to CP2?

    Or is it a case on continually increasing the setting until all the radiators are sufficiently hot?
  6. John.g

    John.g Active Member

    If your boiler has a automatic by pass valve (ABV) then it is recommended that you do not use PP but use the fixed speed or constant pressure modes if fitted so fixed speed 2 or 1 may be more appropriate. What is the Wilo pump used for ??
  7. Tom723

    Tom723 New Member

    The Boiler is a Grant 26-36 Utility Pro. Not sure if it has an ABV? Will change to CP2 and see if that gets all the Radiators hot enough.

    The Wilo pump is for the underfloor heating in our Conservatory. That hasn’t worked all winter but haven’t have the money to get anyone out to look at it. :-(
    • Like Like x 1
  8. John.g

    John.g Active Member

    You probably havn,t a ABV (oil fired boiler). That pump should still be under warranty so should be replaced FOC if noisy at the highest setting, you shouldn,t have to settle for a lower setting and possibly lower rad output because of this.