Suggests to me that the flow is marginal and it's enough for some rads but not for others. Given the relatively recent age of the system and the even more recent boiler replacement I'd not expect it to be seriously sludged up.
I could be wrong: it could be blockages in the pipework, but I'd go for the low-hanging fruit and investigate the pump and diverter properly before going for power-flushing and/or ripping apart the system to flush out the pipework & rads separately.
YAPH wrote on Dec 19, 2009:
That sounds extremely sensible to me. When I can get someone (hopefully reasonably competent) in to look at it I'll suggest that he has at look at these first. Presumably both these devices (pump and diverter valve) are reasonably easy to get at and and somehow check?
Unfortunately it looks as though I'll have to wait till the new year before I can get anyone though - bloody Christmas! Bah humbug etc. :-)
Pump's easy enough: remove end cap, stick screwdriver in slot in shaft and feel if the pump rotates freely. And with the pump running, how much force is needed to stop it. Diverter valve might be a bit trickier: I'd be looking to see how much it travels and maybe try to operate it manually to feel if it moves freely. I'd also feel how quickly heat travels along the main flow & return pipework when the boiler is switched on from cold.
Non-barrier pipe is OK if the system has been properly treated with corrosion inhibitor.
Yep. Just re-dose every 4 years.
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