Yes, that's basically it, have a read of this.
Constant flow automatic bypass valves | Page 3 | PlumbersForums.net
Re your query on condensing effect, it can/will have a effect but this is dependent on the boiler return temp as condensing doesn't begin until ~ 55C. Using a few numbers, if your boiler requires 4 LPM minimum flow and assuming a boiler temp of 70C with a return of 50C and a flow rate of 10 LPM with no by pass, because of the constant by pass you will have 10 LPM at 50C mixing with 4 LPM at 70C resulting in boiler return of 55.7C so a loss in condensing effect, if the flow through the rads was only say 4 LPM (if TRVs fitted) then the return may only be 45C but mixed with the 4 LPM bypass at 70C will result in a boiler return of 57.5C, not hugely different in temperature but a fairly significant difference in condensing effect.
You can see the effect of the different return temperatures here on boiler efficiency.
Constant flow automatic bypass valves | Page 3 | PlumbersForums.net
Re your query on condensing effect, it can/will have a effect but this is dependent on the boiler return temp as condensing doesn't begin until ~ 55C. Using a few numbers, if your boiler requires 4 LPM minimum flow and assuming a boiler temp of 70C with a return of 50C and a flow rate of 10 LPM with no by pass, because of the constant by pass you will have 10 LPM at 50C mixing with 4 LPM at 70C resulting in boiler return of 55.7C so a loss in condensing effect, if the flow through the rads was only say 4 LPM (if TRVs fitted) then the return may only be 45C but mixed with the 4 LPM bypass at 70C will result in a boiler return of 57.5C, not hugely different in temperature but a fairly significant difference in condensing effect.
