Half of the downstairs radiators hot when upstairs turned off

Hi, We had a leak from a couple of valves near the pump, we fixed these but when we turned the heating back on the downstairs radiators stayed cold. My brother is an trainee ex-plumber so he told me to try and balance the radiators. This didn't help.

If I leave the heating on a couple of the downstairs radiators got warm. When I turn the upstairs radiators off about half downstairs get hot.

I have tried flushing the system and refilling thinking there may be an airlock or sludge that has been disturbed but this did help.

We made the mistake of not turning the power to the pump off (well not at first) when fixing the initial leaks and am wondering if I have broken the pump. The pump is an old British gas Multi Head 2 which I don't seem to be able to bleed.

Is it possible that the downstairs radiators are only getting hot via conduction rather than circulation/convection?

Thanks
Phil

 

I have checked the bypass valve and that is set to auto. I still have hot water as well as the some heating so I'm assuming the valve is still working.

 

Hi Ictchyspanner,
Sorry I miss understood your posts,
The bypass valve is located after the pump but before the 3 way port, correct?
This was the valve we changed and I have a feeling we opened it fully. Do you have any suggestions to how open this valve should be?

Thanks for your help