Grundfos Alpha2 15 60 130- Pump speed and noise issue

[Mach13]

Hoping someone might have an answer here....

Moved into the house last year so don't have any installation service/history...
I had an additional rad fitted about 8-9 months ago the pump ran at 45W (way too noisy) when on III and 19W (Quiet) when on II. Just recently British Gas came out to fix a leak on on a bleed valve near the boiler. I've since noticed that the pump sounds a little noisier than before and is running at a lesser power draw.. ie 33W on III (still too noisy) and at 13W on II which is noisier than before but bearable. All rads heat up but it feels a little slow

What else can I tell you?
Boiler is an Alpha CD18R
Boiler stat is set to 6
Its an open vented system with standard hot water tank
The are 12 rads

Primary concern - I'm wondering is 13W at setting II still a reasonable speed rate for this pump to run at for my system?

What might cause the pump to run slower?

Is there anything I can be trying to get it back to its previous speeds?
Thanks in anticipation of your help

 

[D_Hailsham]

I've since noticed that the pump sounds a little noisier than before and is running at a lesser power draw.. ie 33W on III (still too noisy) and at 13W on II which is noisier than before but bearable.

Those power ratings suggest that there is no circulation. The BG engineer has turned a valve off and forgotten to turn it on again. Get them back.

 

[Mach13]

Those power ratings suggest that there is no circulation. The BG engineer has turned a valve off and forgotten to turn it on again. Get them back.

Thanks... i'll probs ring em on Monday, but what confusing me is the rads still heat up ok, if a valve was left closed would the rads heat up?

NB hot water also heating fine

 

[D_Hailsham]

Thanks... i'll probs ring em on Monday, but what confusing me is the rads still heat up ok, if a valve was left closed would the rads heat up?

I thought the same thing. When you say speed 3, I am assuming you mean the one marked III - the outer of the three fixed speeds - and not one of the two constant or two proportional speeds.

Here are the charts for the pump showing (top) the head v flow rate, and (bottom) Watts v flow rate.. Your original data are circled in green and the new in red. The yellow curve on the top chart is an estimate of the "system curve" for you installation. It shows how the pressure drop round the system varies with flow rate. The working point is always at the intersection of the system curve and the selected pump curve. As you can see the power on speed III only drops to 33W when the pump is dead heading, i.e no flow; similar for speed II.

 

[Mach13]

I thought the same thing. When you say speed 3, I am assuming you mean the one marked III - the outer of the three fixed speeds - and not one of the two constant or two proportional speeds.

Here are the charts for the pump showing (top) the head v flow rate, and (bottom) Watts v flow rate.. Your original data are circled in green and the new in red. The yellow curve on the top chart is an estimate of the "system curve" for you installation. It shows how the pressure drop round the system varies with flow rate. The working point is always at the intersection of the system curve and the selected pump curve. As you can see the power on speed III only drops to 33W when the pump is dead heading, i.e no flow; similar for speed II.

View attachment 212394

Hey thanks for that detailed info, yes it defo looks as though the current flow is weirdly on the zero.. so strange.. I've turned it off for now and will see what BG say first thing in the morning. They came out pretty quick last time....

will post back when I get further along..

 

[Mach13]

So BG are gonna come out tomorrow... Had a frost last night so it was quite cold when I turned the heating on to monitor it.. it took about 30 minutes before all the rads were feeling some heat. about 50 mins before they were all hot.

Any idea how long it should take to heat to this point normally?

 

[D_Hailsham]

That's a length-of-string type of question.

If the system has been properly balanced all rads should heat up at the same rate. It should take about 10 minutes to raise the room teemperature by one degree.

Apart from a closed valve, another more likely possibility is an airlock in the system. The water would not be pumping round but the heat would move round due to natural circulation - hot water rises as it's lower density etc.

 

[Mach13]

Hurrah so its resolved!

BG came and the engineer removed the pump... turns out the impeller was sludged up with a coating of crud. She cleaned it off reinstalled and it now runs sweet and like a dream... Full speed on all settings without any of the noise that I had before.


Go figure...

All the comments much appreciated folks..

 

[D_Hailsham]

Thanks for the good news.

The pump should now work OK on fixed speed II; III is definitely too high. But it might be worth trying PP speed 2 or even Autoadapt.

It would also be a good idea to balance the system, which should be done on fixed speed II with any TRV heads removed. (See attached pdf, which was written by a Grundfos engineer.)

 

[Mach13]

Thanks will take a look

 

[MJN]

It would also be a good idea to balance the system, which should be done on fixed speed II with any TRV heads removed. (See attached pdf, which was written by a Grundfos engineer.)

Forgive me digging up this old thread, but I've just stumbled across it and was intrigued by the guidance in the attachment:

If the differential temperature is too low, slightly open the lock shield valve; and if the differential temperature is too high close the lock shield valve slightly.

I always thought (and with albeit limited experience) that it was the *opposite* of this i.e. if the temperature drop across the radiator was too low then you close the LSV even more (to decrease the flow; allow more heat to be extracted before it passes through) whereas if if the drop was too high then you'd open the LSV up (to increase the flow; reduce the heat being extracted).

In a knowledge contest between a Grundfos engineer and me my money would be on the former, but can you/anyone confirm he's definitely right? Perhaps I'm just in need of my morning coffee to kick my brain into gear.

P.S. Great to see your username @D_Hailsham and that you're still contributing - I always enjoyed the discussions about the inner workings of the CM927 control logic, optimum start etc which must've been around 10 years ago now!!

 

[Mach13]

just to finish this one off... I've found the culprit or rather culprits... I took the front off the pump to get to the pump impeller and found it crudded up with sludge and all of this (see pic)

. They're a little like crusty carbon pieces that catch n block up the veins and so reduced it's pumping capacity and throwing it off balance, hence the noise. Not sure whether they are from the very old rads (likely) or the boiler. Either way i'm getting new rads installed at some point.. but the pump has since run like a dream... quiet and at its regular pumping power.

So if in doubt check n clean it out...

But thanks again to all those that offered comments they've all been very helpful to reduce that flatten that learning curve.

 

[D_Hailsham]

I always thought (and with albeit limited experience) that it was the *opposite* of this i.e. if the temperature drop across the radiator was too low then you close the LSV even more (to decrease the flow; allow more heat to be extracted before it passes through) whereas if if the drop was too high then you'd open the LSV up (to increase the flow; reduce the heat being extracted).

I hadn't noticed the discrepancy. You are correct in saying that the LS valve has to be closed to reduce the flow and increase the differential, i.e the difference between flow and return temperatures; and vice versa.

The language is confusing - temperatures can be high or low; differentials can be large or small. All I can assume is the author really meant to say that if the return (not differential) temperature is too low, slightly open the lockshield valve, etc"

 

[MJN]

The language is confusing - temperatures can be high or low; differentials can be large or small. All I can assume is the author really meant to say that if the return (not differential) temperature is too low, slightly open the lockshield valve, etc"

Yes, you're probably right. All too easy to get things backwards, the subject is like working with double negatives at times (or should that be not unlike?!).