Radiators not heating , poor circulation?

[Olivias Grumpy]

Thanks for that info.
There 2 other settings I think CP1 CP2 ? Would these be more suitable as the pressure is supposed to be more constant even if load changes?
If not, I could use III. The original Grundfos 15-60 was set to this

Cheers

 

[Terry lambert]

Yes, start with C2 with an auto by pass

With proportional pressure as resistance increases the pump will back off to as much as 50%,
With proportional you should have a fixed by pass ( not efficient) or a flow setter set to maintain the minimum flow required

 

[Olivias Grumpy]

Hi
I've found some info on the boiler and manual says min flow to be maintained is

maintain a minimum flow through the boiler of 4.5 litres/mm (1
gal/mm)

Is this correct? i thought it would be expressed as litres/minute

 

[jackthom]

Its a misprint or if it's a PDF taken from a scanned document it could be an OCR error.
It will be litres/min.

 

[Olivias Grumpy]

Thanks for that.

It was from a downloaded manual direct from potterton
It’s been wrong since day 1

 

[D_Hailsham]

If you use a CP setting there will be a constant flow through the bypass, even if it is an automatic bypass which will have to be permanently open; thus defeating the purpose of an ABV.

You said that the old pump was a 15-60, set to speed 3. This seems very high for a system with 13 rads and a boiler with a very low resistance. (I have 13 rads and a modern boiler with a high resistance; my UPS2 is set to speed 1.)

I note you have tried to balance the system, but with limited success. What procedure did you follow?

 

[Olivias Grumpy]

We tried lots of different ways before we changed the ABV
When it had been changed we took a long time bleeding , running system cold then bled again
Turned off ground floor rads
Turned on up rads and heated
Turned lockshields down on up rads to about 30% open
Then turned on ground floor 1 at a time, when each one warmed closed lockshields to about 50%
Hall rad where room stat is lockshields are at about 60%
Rear kitchen rad and a lounge(kids room) fully open. (Still not hot but warmer than before we changed ABV)

I now think I could improve by tinkering with pump speed and finally ABV setting

However I am getting confused with differing views.

 

[Terry lambert]

http://www.newtonnet.co.uk/permanent/GrundfosDocs/BypassCommissioningAlpha2or2L.pdf

 

[Olivias Grumpy]

Thanks Terry
Now I’m getting confused
But if I have read it correctly it confirms that I should be using CP2 with ABV. OR use Proprtional Control and a fixed bypass?

Boiler min flow is 4.5 l/m
Can you take an educated stab at ABV setting based on CP2 pump setting?

Then I can start on his/their next problem. Condensation in former windows.

 

[Terry lambert]

Between .3 to .35

I havnt got the chart for your valve so have worked off of another chart, start with .3 and if you get excessive noise when a demand for heating and hot water has stopped, adjust the valve open slightly more

 

[Terry lambert]

Could have saved you the trouble of two threads but then you wouldn’t have had this much fun

 

[Olivias Grumpy]

When all else fails a lot.
Thanks for your patience
I’ll try it in the morning

And I’ll still try and calculate it cos I’m stubborn and I like problems to sort!

 

[D_Hailsham]

Boiler min flow is 4.5 l/m

The normal flow, when boiler is working is 23 l/m. So you are sending through the bypass approx 20% of the energy generated by the boiler. If you use a CP setting, 20% will be lost all the time.

You have two options:

1. Run the pump on a fixed speed and set the ABV so it is normally closed and only opens when necessary, e.g when TRVs close or zone valves close.
2. Run the pump in PP mode and install a fixed flow valve after the ABV. When the ABV is closed there will be no flow down the bypass; as the bypass opens more and more the flow will be restricted by the fixed flow valve. Grundfos recommend the Taconova Setter, which has a flow gauge so you can adjust the flow accurately. You need the correct one for your flow rate of 4.5 litres/min

Do you have an Alpha2 L 15/50 or 15/60? This will determine the correct setting.

 

[Terry lambert]

@D_Hailsham

I cant think of a single perfect solution for pumps on constant pressure or on proportional

On constant pressure the ABV will still always be open and letting by if set correctly the minimum flow of the boiler at pumps set pressure, which as the name suggests will be constant regardless of what is happening in the system

On proportional a flow setter would be better than a fixed bypass as you can set the minimum flow for the boiler accurately

All options will be letting by to the boiler when in operation that I can see, unless I’ve missed something

 

[D_Hailsham]

I cant think of a single perfect solution for pumps on constant pressure or on proportional

An ABV with CP is useless. It is impossible to set it correctly, unless you have a flow meter, as the pressure is constant. So you have to set the ABV to open at a lower pressure than the pump. (If the ABV is set higher than the pump it will never open.)

An ABV, on it's own, will not work with PP as the valve will open more and more as the pressure rises, meaning more flow through the bypass.

The suggested solution is to put a flow control valve after the ABV. When the pressure is lower than the ABV setting the valve will be closed, so no flow through the bypass. When the pressure is higher than ABV setting the valve will open and there will be flow through the bypass. The pressure may rise further, opening the ABV further, but the flow will be restricted by the flow control valve.

Grundfos recommend this solution in the Bypass Commissioning document you linked to earlier.