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Discuss Grundfos Alpha 2 does not self prime in the Central Heating Forum area at PlumbersForums.net

Richard Chambers

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I have replaced a 15 year old Alpha + with a Alpha 2 15-60. It is positioned 1.5m above the boiler( feeding a 10 rads and hot water on S plan), in the attic with a 0.5m head from a header tank.
I am having great difficulty getting the new pump to self bleed. Setting it to constant fastest speed, it doesn't 'suck' hard enough to clear the air. I have had to replace the header feed with a temporary mains pressure (3 bar) input to clear the air after which it runs fine.
Any suggestions, thanks.
 

chris watkins

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Have the system converted to a seal one, it really is beneficial to loose the F&E, Richard.
Circulators are not very good at sucking, they push & so are no good at getting water to clear air from pipes.
 

Millsy 82

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Put a thumb vent on the highest part of the system.

Dobt the alphas have a bleed screw behind the control box?

I wouldnt say change the system to a sealed system. As long as its piped right a vented system works perfectly well.
 

John.g

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Put a thumb vent on the highest part of the system.

Dobt the alphas have a bleed screw behind the control box?

I wouldnt say change the system to a sealed system. As long as its piped right a vented system works perfectly well.
I think if the label descriptor has a "A" at the end (ie Alpha 2 15-60 A.) then a air separator can be fitted so presumably has a bleed screw fitted in this position.
 

Craig Watson

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The alpha 2 doesn't self bleed, you have to remove the black head unit to get to the bleed screw. Go on YouTube and search how to bleed alpha 2 pump and it shows you how.
 

ShaunCorbs

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The alpha 2 doesn't self bleed, you have to remove the black head unit to get to the bleed screw. Go on YouTube and search how to bleed alpha 2 pump and it shows you how.
You’ll break it popping it off tho
 
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Richard Chambers

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Thanks for all the comments and suggestions. I have turned the pump to run vertically now and added a bleed vent at the top on the outlet side so it completely vents now. I saw the video about removing the control unit but didn't in case it broke - no warranty then.
I shall swap the manual bleed points to Calaffi auto vents too.
I am still thinking about the sealed system option.
 

John.g

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You would seem to be getting continual air ingress since changing this pump?, not having a pump vent should only be a nuisance until all the system air is/has been vented. There are numerous posts on here from people who had problems with air ingress when renewing the circ pump on vented systems which can be very sensitive to pump head.
IF you are still running on fixed speed setting 3 which is a 6M head on this pump then IMO you will certainly tend to get air ingress in a vented system. You might post the present pump mode and speed setting, you should be able to sort this out without installing a sealed system.
Any idea what the old pump speed setting was?.
 
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Richard Chambers

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I have now got the pump working properly, but the old pump would purge at Speed 3, and then I would run it at 'normal' plus a bit. I am replacing the old one as it had got noisy and the speed control had stopped working.
The new pump runs at CP2 and can show up to 45W, but normally about 35W. There is a very small trickle coming up through the safety expansion pipe into the tank at 45W but not normally. There is also an automatic by-pass set to position 3 (Honeywell DU145).
I have experimented with the other settings. AutoAdapt uses least power but doesn't give enough flow.
 

John.g

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Thanks Richard,
It's interesting that its running at 35W normally which, according to the pump curves is a flow rate of (2 M3/hr) 33 LPM @ 3M head, this seems a very high flow rate for 10 rads, one would expect ~ 12/20 LPM, my own 10 rads+HW circulate @ 12 LPM @ ~ 3M head, your ABV setting is 3M, the same as the pump CP2 setting of 3M, is it possible that the ABV flow rate is excessive even though theoretically at least it should be circulating zero. All this circulation, if happening, can lead to problems with air ingress due to expansion pipe pump over and pump cavitation especially in a vented system. ABV's are not recommended for pumps running in PP mode, a fixed orifice is the recommendation. However, if you're system is now running OK then ?.
Its also very interesting that the pump occasionally pulls 45W despite a rated max power of 34W.
For info, my system runs at 18/21 watts with everything opened up on a PP setting of 4M (Wilo 6M pump) which results in that flow rate of 12 LPM @ ~ 3M head.

Edit, above, should have said that a ABV is not recommended in PP mode only.
 
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Richard Chambers

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That's a very detailed input! I think the power discrepency is due to the fact mine is an older pump - see the attached chart Annotation 2019-07-22 151745.png which does show 45W as the max power.
My system is a couple of 22mm feeder circuits ( up and down) supplying 8mm micro bore to the rads, if that makes a difference.
I maybe using too great a flow to ensure the more distant rads heat up properly. I expect I could do a better balancing job. Some of the 8mm pipework is quite long as it's a 500 year old house and not easy to run pipes.
I shall try reducing the flow again, but it is pleasingly quiet.
Thanks again.
 

John.g

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That explains the power then, any idea what the ABV is doing with its set point the same as the pump setting?, is it passing continuously or not at all?, if its purpose is to provide a flow on boiler shutdown/pump overrun or/and to provide a minimum flow through the boiler then it must have been set up sometime as a small change in its setting can result in a big flow through the ABV.
 
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Richard Chambers

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I don't believe there is any flow though the ABV, and I was not convinced I needed one but it was fitted when the boiler was installed. It's a Grant oil boiler, that doesn't do overrun. The CH does have a couple of non thermstatic rads, so there can be flow even if the house is hot and the room stat is v high. I think I turned it up many years ago, from 2 to 3.
 

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