Pump speed ?

[OldEV]

I have a Worcester Greenstar 18Ri with a Wilo RS50 pump on an open vented system, the pump as approximately 2 mtrs of head.

I've been advised to keep the pump speed set at 2 to maintain the correct flow rate through the boiler, however with the pump set to 1 it is obviously much quieter and all the radiators still function properly.
I can't seem to find the flow rate required by the boiler or the flow rate produced by the pump at it's three different settings.
Am I safe to run the pump at it's lowest setting or must I keep it on 2?
Any advice on this would be appreciated.

 

[Biguns]

Slowest speed possible, whilst not affecting radiator performance

 

[D_Hailsham]

I can't seem to find the flow rate required by the boiler or the flow rate produced by the pump at it's three different settings.

The flow rate of a pump is not constant at each speed; it depends on the head (friction of the circuit). Here is an example of a pump curve:

Change of pump and boiler 1

• D_Hailsham
• 7 Jan 2010
• 2

The three black lines are the three speeds. When you set the speed the pump always works along the relevant line. So, if the circuit head is high, the flow rate will be low and vice versa.. Because most pumps are fixed speed, you always have to compromise. Use the lowest speed which gets all rads equally hot.

A properly balanced system will run at a lower speed.

If your boiler keeps cycling (stopping and starting) it could mean that the boiler is giving off to much heat and needs to be down rated.