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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.
 
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.
 
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.
 
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
 
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.

This attachment must be the latest line up of models that incorporate a air chamber.
 

Attachments

  • Grundfosliterature-3980922.pdf
    8.3 MB · Views: 22
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.
 
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?.
 
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.
 
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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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.
 
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.
 
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.
 
Just a few final thoughts, in view of the fact that you don't need a ABV, why not consider just winding it up to say 4 or 5 on the index to ensure no possibility of activation under any conditions?. Re your first post, you said you ran the pump at speed 3 to try and clear the air, if the ABV was still at this 3M setting then there was a good possibility that it was recirculating and not helping to get rid of the air. Finally, at approaching 45 watts there is little difference in head/flow between CP2 and PP2, you did say that expansion pipe pump over tends to occur at 45 watts but it just may be worth/interesting to change over to PP2 after winding up the ABV setpoint and compare pump power(s).
 
I have done that now, and set it to PP2. The power usage is interesting
Annotation 2019-07-23 130118.png

This is with the off, the numbers increase a bit for being on.
he only bit I don't understand now is 'Head'. My pump and boiler are at the top of the house, with a max of 6m from the lowest point to the F&E tank. The data suggested about 3m head?
Thanks for your help.
 
The only bit I don't understand now is 'Head'. My pump and boiler are at the top of the house, with a max of 6m from the lowest point to the F&E tank. The data suggested about 3m head?
'Head' has nothing to do with distance. It's a way of measuring pressure. Look at the graph for your pump and you will be that the vertical axis is labelled "P (kPa)" as well as "H (m)". The pressure is that due to friction in the circuit, i.e pipework, rads, valves and the boiler. The pump has to create sufficient pressure to overcome the pressure drop round the circuit.

Pressure is proportional to the square of the flow rate, which is inversly proportional to the temperature differential. So a system using a 20C differential will have half the flow rate of one with a 10C differential, and consequently the pressure drop will be a quarter that of a 10C differential.

Height is irrelevant as it is a closed system.

It really is about time the heating industry dropped the use of "head" to refer to pressure drop. It's archaic.
 
I have done that now, and set it to PP2. The power usage is interesting
View attachment 39651
This is with the off, the numbers increase a bit for being on.
he only bit I don't understand now is 'Head'. My pump and boiler are at the top of the house, with a max of 6m from the lowest point to the F&E tank. The data suggested about 3m head?
Thanks for your help.
Very interesting,
I have done that now, and set it to PP2. The power usage is interesting
View attachment 39651
This is with the off, the numbers increase a bit for being on.
he only bit I don't understand now is 'Head'. My pump and boiler are at the top of the house, with a max of 6m from the lowest point to the F&E tank. The data suggested about 3m head?
Thanks for your help.
Very interesting, now if your present installed pump curves are as per post #13 it means that the CP2 setting is 4.5M and IF you had a ABV setting of 3M then there would have been a huge bypass through it, now that you have increased its setpoint up to MAX to allow no by pass at 4.5M head then there is IMO a greater danger of pump over now because the pump probably wasn't achieving that 4.5M head with that huge flow. You can try it, ABC set at 6 and CP2
(4.5M) and look at the expansion pipe re pump over. Using your your readings on CH...SP2 = 15 [email protected]. PP2=17 [email protected]. CP2=27 [email protected] and CP1=19 LPM@3M, if you have no problems with CP2 when boiler is firing etc then you may decide to leave it there, if not (and getting pump over at any condition) I would suggest CP1 or PP2 and see if all the rads are heating up OK as the flow rate will now have fallen from ~ 27 LPM to ~ 18 LPM but may be still quite adequate and may actually improve the boiler efficiency due to a lower return temperature.

"doityourself" has answered your second query, another way of explaining it is consider having a inverted U tube full of water of any height, say 20M with one end connected to the pump suction and the other to the pump discharge with a pressure gauge at both ends, with a stopped pump both gauges will read exactly 20M (the head), if the pump is now started then the pump discharge head will rise and the pump suction head will fall, the difference in these is the pump circulating head or pressure loss and depending on the system resistance will give a certain flow rate depending on that differential head.
 
With rads only on and assuming they are emitting/absorbing that 23 kw then a flow rate of ~ 18/20 LPM should give a rad(s) delta T of ~ 17C so either PP2 or CP1 might do the job.
 
With rads only on and assuming they are emitting/absorbing that 23 kw then a flow rate of ~ 18/20 LPM should give a rad(s) delta T of ~ 17C so either PP2 or CP1 might do the job.
There are only 10 rads in the house, so I doubt if they add up to 23kW; probably not much more than 15-20kW. As oil boilers do not modulate, the boiler will be cycling wth a 65/35 on/off period.
 
Yes, probably correct there, so in general, IMO its better to keep a reasonably high flow rate which should help to reduce cycling because of reduced deltaT through the boiler and taking longer time to reach cut out temperature.

Something else that caught my eye there in the numbers, see attachment, if you look at the head/flowrates for CP2 and CP1, CP2 is showing a flow rate of 0.95 m3/[email protected] and CP1, 1.1 M3/hr@3M, maybe I'm reading the curves incorrectly but for the same system resistance these two readings are incompattible?, a flow of 1.1 M3/h@ 3m = 1.35 M3/[email protected] or 0.95 M3/[email protected] = 0.78 M3/hr@3M.
 

Attachments

  • Grundfos Alpha 2 Composite Richard.zip
    189 KB · Views: 3
There are only 10 rads in the house, so I doubt if they add up to 23kW; probably not much more than 15-20kW. As oil boilers do not modulate, the boiler will be cycling wth a 65/35 on/off period.
You are correct, the Rads are about 16kW and the HW is 14.5kW. So I do get a bit of cycling. The excess covers the overlap when both are calling for heat. I have run the boiler at 19kW, but when the smaler burner burnt out, it was replaced with the std one which then give 23kW. Maybe I should consider the saller burner at the next service.
 
You could go for the smaller burner, only downside is a longer heat up time on a cold morning if the boiler has been shutdown overnight, cycling doesn't seem to have a big effect on boiler efficiency if one can believe the numbers I've seen. I have a 20kw oil fired (Firebird) and the only time it cycles rapidly is on HW only when the water temperature is approaching 60C when the coil is probably only absorbing 2 or 3 kw, but the coil only absorbs 7/8 kw from cold.
 
Something else that caught my eye there in the numbers, see attachment, if you look at the head/flowrates for CP2 and CP1, CP2 is showing a flow rate of 0.95 m3/[email protected] and CP1, 1.1 M3/hr@3M, maybe I'm reading the curves incorrectly but for the same system resistance these two readings are incompattible?, a flow of 1.1 M3/h@ 3m = 1.35 M3/[email protected] or 0.95 M3/[email protected] = 0.78 M3/hr@3M.
Where do you get your numbers from:

1. Top table?
2. Middle table?
3. The graphs (estimated)?
 
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The (very) top table (composite file) are my results from the below:

I used the power (watts) values from Richard's readings ( table), I then went to the bottom chart and where the power (vert.axis) met the pump curve(S) I read off the flow rate in M3/hr (horiz axis), I then used these flow rates in the top chart (horiz axis) and where they met the pump curves I read off the head in M (vertical axis).
The table in that composite is more correct than the ones in my post, above.
 
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The (very) top table (composite file) are my results from the below:

etc etc
I thought that's what you had done; just wanted to be sure.

Don't forget that when the pump is in a constant pressure mode it will vary the output to maintain the required pressure. The fact that the pressure may be too high or too low is irrelevant.
 
As this is proving so interesting, maybe I could ask a supplimentary question. I have always had a problem in the winter with cool rads when the both the CH and HW are calling for heat. I have now fitted a gate valve to act as a restrictor on the HW tank.
Should I restrict the flow into the tank so that the power W reading is the same for CH only and HW only of say PP2, given they both have approx the same power rating? Or just screw it in half way. The HW circuit is very short and all 22mm whereas the CH is 22mm into 8mm to the rads.
Thanks
 

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