Alpha 2 Pump

[btkippers]

Hi guys,

Currently have a Grundfos Alpha 2 Pump running on a Potterton Prima F boiler with the pump running in an auto adapt setting. Looking to replace existing boiler but concerned about kettleling, the Alpha 2 pump's lowest setting is 8W on my system. I am unaware of what the flow rate would be at 8W and as such have been unable to pick out a suitable boiler, can anyone recommend something that could cope with such a low flow rate?

Have spoken to a few of the big manufacturers but they are either unwilling or unable to help with any practical advice. All opinions grateful received, thanks in advance.

 

[gas4you]

I personally don't like any pumps such as these. They will work at what level they think they should, rather than what is best for the boiler.

Swap to a system boiler and dump the pump

 

[David937]

I personally don't like any pumps such as these. They will work at what level they think they should, rather than what is best for the boiler.

Can an example be the Vaillant 400 series which I understand work best at higher pump speeds?

 

[gas4you]

Yes it can

 

[D_Hailsham]

You don't select a boiler to match the pump; you select the boiler to give the right heat output for your house. Use the Boiler Sizing Wizard

Currently have a Grundfos Alpha 2 Pump running on a Potterton Prima F boiler with the pump running in an auto adapt setting.

Which Alpha 2? 15-50 or 15-60 etc
Which Prima F - 30, 40, 50, 60 80 or 100?

Prima's can also be gas rated, i.e each version can be adjusted to cover a range of output. For example the 30F can deliver between 5.86kW and 8.69kW.

Alpha 2 pump's lowest setting is 8W on my system. I am unaware of what the flow rate would be at 8W

The flow rate will depend on which Prima F you have and how it has been rated- see question above.

Measure the gas flow at the meter for two minutes and post the results (and the boiler version).

have been unable to pick out a suitable boiler, can anyone recommend something that could cope with such a low flow rate?

Just because the pump is only using 8W does not mean that the flow rate is necessarily low. It all depends on the pressure loss (head) which the pump has to overcome.

 

[btkippers]

Thanks for the help so far guys, will check for the information you have requested and post it up asap.

 

[Boilerman2]

I have serious resevations regarding these so called energy saving pumps,

1) they cost three times that of a standard pump
2) they try to dictate the flow rate (how the hell can you design a system with a pump that does whatever it likes?)
3) They still burn out after 3-5 years and have to be repalced!!

I don't think they are worth the money

 

[D_Hailsham]

2) they try to dictate the flow rate (how the hell can you design a system with a pump that does whatever it likes?)

The fixed speed pumps can be just as bad. You need the pump set on 2 to give the correct differential across the boiler; but it needs to be on 3 to make the rad farthest from the boiler hot.

In any case, I think you are wrong in suggesting that the pump tries to dictate the flow rate. It adjusts the pump speed to give the correct flow rate at the given head. I don't know exactly how it does this - the patents are in Danish - but it looks as if the pump contains sensors to measure the differential pressure across the pump, the flow rate and the flow temperature.