Cold radiators balancing

[JoeBilton]

Our upstairs radiators were getting much hotter much quicker than down stairs. To try and balance I altered some of the lock values on the upstairs rads (not fully closed though) this seemed to work and the downstairs rads were much hotter however one of the upstairs rads was now totally cold. So I’ve opened up all the lock valves and TRVs on all the radiators but to no effect and now not only is the upstairs rad still cold but the rad downstairs furthest from the boiler has now also got no hot water going into it. Checked the TRV on the cold rad and the pin pops up as normal so assume this is working fine. All the radiators have been bled and the pressure on the boiler is at 1.5 - any help you can offer would be most welcome

 

[ShaunCorbs]

Did the one work before could be a sign the pump is getting weak

 

[rcpilot]

or the pipes have managed to block up somewhere

 

[Ben-gee]

Rather than open up all the lockshields and trv. Close all the trv except the upstairs problem rad - does it now get hot?
Do the same with the problem downstairs rad - hot?

If so it I’d probably a balancing problem, do go through this methodically from the start
If this doesn’t yield results, look at the pump