CH-pump speed

[desktop987456]

My old gas fired boiler has 3 settings, I ran the central heating for 2 hours to observe boiler cycling at lowest pump speed setting; it will fire for 7-8 minutes and when preset temperature setting is reached it will switch burner off for 10 minutes and cycle continues. It consumed 2.1m3 of gas in 2 hours as per utility meter.
I then switched the pump setting to medium and burner will come on for 5.5 minutes and idel time of 11 minutes. The radiators emitted even heat in low pump speed setting, my question is why low pump speed setting consuming more gas? Thanks in advance.

 

[cross thread]

Was the second test in the same conditions ?

 

[desktop987456]

Thanks. I started the boiler at1615 hours and took reading at1815 hours. The second test ran from 1815 - 1915 hours. I don't know the outside temperature but it must have been colder for second test. When I increased the pump speed to medium setting I also reduced the temperature by 2 degrees; could it have an effect?

 

[Mottie]

Surely you need to get the house up to temp and carry out the same test at different speeds to get a true comparison.