Cold Radiators

[Endulini]

Hi All,

I have an issue with a couple of my downstairs radiators in that they never seem to warm up completely, namely they are cool at the bottom and warmish at the top (but never toasty). I'm reasonably sure that it isn't due to sludge as I've flushed the system a couple of times with cleaner and the water drained from these rads was never dirtier than I'd expect (one is a particularly large rad 2-3m long). Also. the local heating engineer who has some experience of the system maintains that they were power flushed 3 years ago (before I bought the house) and that the poor heating is more likely due to the narrow bore pipework used in the system. He has fitted a larger pump upgrading from a 15/50 to a 15/60 but that doesn't appear to have made much difference and reckons pressurising the system should sort it (the boiler is suitable for this approach). Before I go down that path I was contemplating what other options I could try, could it be as simple as rebalancing the system or is there anything else to consider?

If it helps, it's a five bed house although not what I would consider unusually large :)

Thanks

[The Natural Philosopher]

WEll obviously shutting down all radiators except the two in question to see if they get hotter is a good place to start.

If they don't it suggests that the flow is severely restricted. And unless the pump is cavitating I don't see how increasing system pressure will increase flow rate.

[Andy Burns]

if you close off all other rads, do the "cool" ones ever get get hot?

[newshound]

I had a problem like this with narrow bore (10 mm) piping to a main radiator downstairs. In the end I stripped it out right back to a manifold above the ceiling, and re-plumbed it in 15 mm. I strongly suspect that there was either a kink in the pipe somewhere (it had difficult routing through 1700's oak structural timber) or a pool of solder somewhere inside a coupling, although I never located the exact cause.

[Endulini]

Shutting off all the other rads means the two in question get nice and toasty - so this is a balancing issue? How do I go about balancing the system?

[Andy Burns]

Maybe, what happens if you open up more and more of the radiators? Does one in particular "hog" all the heat when it's on? either close lockshield on the hog(s) down a bit, or open up the lockshield on the cold ones ...

[Roger Hayter]

If that won't work, is there any reason why you might need a higher flow rate in the whole system rather than a higher pressure? Such as lots of fan assisted radiators or a very large number of radiators. Then you can find that however you balance it you always have some relatively cool radiators. In this situation I got a standard fitting flow pump with a 25mm rather than 15mm capacity, but standard sort of pressure. E.g. 25/60

But really if it is not an unusually big or high flow system a few iteration should balance it. Just make sure all the radiators can be turned off with the lock shield valve and there isn't one jammed open near the boiler. Or an excessively big bypass pipe/towel rail or something.