How do I diagnose a faulty pump?

[soundsalarming]

I have a problem that seems to be shared with a few others on this forum, "cold downstairs radiators".

The advice seems to be , bleed the system, clean the system, check the pump. Well I bled the system, and the water was crystal clear which suggests to me that the system is sludge free.

If this is right, the only thing left is the pump, but how do I check its operation?

 

[oilman]

You may have crystal clear water, but its coming out of the top of the radiators, and the krud is heavy and sinks to the bottom. try draining a little water out of the drain cock on one of the downstairs pipes and see what that looks like.