Rad slow to heat up - but gets there

[Martino]

Hi,
CH system powerflushed, balanced, new pump, and new 3 position valve a couple of weeks ago. Everything working fine - rads all scalding, boiler quiet etc. Bliss. Then suddenly today just one radiator is taking longer than usual to heat up. If I put the heating on for a single hour it takes most of that hour to get to very hot but not quite to scalding like the other radiators are. If I leave it on longer it continues to work up to scalding, although there is a heat difference between the top/inlet side and the bottom/outlet side.

I did the obvious and bled it but no air found and as it was heating up top first I assume it's not air anyway.

Any suggestions as to what could suddenly cause this slow heat up and how to fix it? I'm wondering if a bit of loose crud from the powerflush is blocking something but it heats up in an obvious order if that makes sense - top and side nearest inlet first, bottom and side nearest outlet last (gets very hot but not very hot) and doesn't stay cold at the bottom. Also, why would it take 2 weeks to suddenly do that? Or does crud travel slowly?

It's the radiator in the hall so the one most likely to impact the room stat so I'm worried it may leave the system pumping away unnecessarily when it's hot enough in the rest of the house.

Or am I just being paranoid and impatient?

Thanks.

 

[mogget]

It may be a bit of crud caught in one of the rad valves, or some air in the pipes associated with that radiator. Close the lockshield valve, taking note of how many turns it takes. Then open both valves fully, and if you have TRV's on the other rads, turn them to the lowest setting. Run the heating for 10mins or so before putting all the valves back to where they were. If you're lucky this should sort it out. Otherwise post again, we'll have to dig a bit deeper.