hot water for central heating not circulating

[ChrisR]

Get him at least to look at the pump. They can get clogged so they're doing nothing at all.

Also it shouldn't be too easy to stop. If you can do it with your little finger it's probably due for replacement.

My Yellow Jacket doesn't say Gas, by the way, just
"In Charge".

 

[ChrisNason]

Thanks Chris. How did your plumber locate where the bad pipe was?

He spent some time over coffee working it through with me. We knew that the return was nearly stone cold, the feeds to the radiators were scalding, the flow from the boiler was scalding, the flow from the motorised valves was scalding and the return from the Hot Water Cylinder was stone cold.
He just thought that it was a blockage and the most likely point was where pipes joined each other. He first cut out a section from the return to the boiler just to see what was in it. He then looked at a radiator before going for the group of pipes.