When my system was recently updated (converted to a sealed system), a bypass pipe and valve was fitted near to the pump. I didn't have one before and I understand that the bypass is there in case all rads shut off with thermostatic valves and the bypass allows the water to continue to circulate until the boiler cools sufficiently to prevent overheating.

Of the 10 rads we have fitted, 3 of them (bathroom, top landing and front room) have no thermostatic valves fitted so, unless someone switches them off, will never be closed.

Is it therefore ok to close the bypass valve as I've read on line that it can give a quicker system warm up? Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

I am not a heating engineer, but I do have a similar system. I always understood that there should be at least one rad permanently open without a 'stat. Ideally situated nearest the roomstat (if fitted). As the system has recently been updated I am surprised you have 3 rads without.

Regarding the by-pass valve, if it is an automatic type, you should not need to touch it. If it is simply a manual gate valve, it will be set to a small aperture, offering some resistance to flow, giving priority to the rads.

Bob 10MY (Sept 09) TD4 HSE Auto in Stornoway Grey (Now Gone)

08 FL2 TD4 SE Manual in Rimini Red (Now Gone)

close the bypass let it cool then open the bypass very slowly until it allows heat to pass back to the boiler then leave it alone