I have a Myson CH pump and I have a question regarding pumps in general. My
pump has a 3 position switch marked I, II and III this switch just seems to
alter the speed. Is it better to have the pump set at I (slowest) so that
the water passes over the burners slower so heats up more, or set at III
(fastest) so it gets round the system quicker or II (Middle) so it gets the
'best of both'? There must be a reason for the switch or it would just run
at one speed!

Cheers

John