poor circulation, check filter mesh may be blocked after draining boiler open cap on front end of return boiler isolation valve and check filtermesh and clean as necessary and re fix back and try.
k
October 2012
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.