Has anybody come across same problem as i have. Just moved into new house central heating playing up,rads upstairs getting hot downstairs cold.Had corgi reg guy out changed control switch new three way valve and new pump drained the system and filled it from bottom rad but had rads warm not red hot .Since then rads down stairs cold again plus reset button keeps tripping out and when you stop pump you can hear it bubbleing up does any one know how to fix problem thanks