New Rad, Hot at top, cold at bottom

CBYR1983

As per title.

Can't understand it - it's an upstairs rad, couldn't be sludge surely, it's only in a few months. Don't think it can be air either - could it?

Forgive my ignorance, but I've read that it could be balancing. I don't understand this though, as I thought the whole rad would be affected by balancing, not just the bottom. Can anyone explain?

JohnnieK

It has to be a blockage. If the rad was put on a dirty system it can still sludge up, and it would take a few months.

Buford T Justice

Sludge. Had the same problem with my system. Was there an inhibitor put into the system when it was installed?

K.Flyer

If the system was flushed before the new rad was fitted then it may be a case of the system needing re-balancing or you may have an airlock on the flow pipe to the radiator. If its an airlock try shutting off all of the other radiators and just leave the one giving trouble on. You may hear some gurgling sounds from the rad, as air comes through. If the rad then heats up fully turn back on all the other rads and see does it then stay hot. If it cools back down then the system probably needs rebalancing, best to call in a good plumber as its a bit trickier to explain all the details.

Sparkpea

Likely sludge as people say. If the system was dirty when it was installed then its only going to block again. You would be best getting the system powerflushed (cleaned out properly) as it cures most circulation problems. The only other possibility is that if its at the end of the line then it could just be slow heating at the bottom if the pump is old and the motor wearing down, to check this turn off most of the radiators except this one and leave it on for a good hour before checking it.

CBYR1983

Thanks Lads,

I will try to turn off other rads and see how it goes.

I wanted to have the system flushed - the whole system had all been drained down but plumber reckoned there no need for power flushing - afraid to cause leaks as there is some old piping there. Most of the piping is stainless steel, but there is some Gunbarrel.

I think it could be sludge, but maybe rebalancing would help dislodge it.

There was always one radiator upstairs that never heated properly before - I explained this to the plumber and he told me he had got it to heat - but I think he did so at the expense of the other rads upstairs.

As part of the re-work I put in a number of doubles upstairs where there were singles but replaced all rads downstairs as well, putting on TRVs.

One further issue is that all 4 upstairs rads are fed by 1/2 inch piping. It could be that it is just taking so long to feed these upstairs rads, though the downstairs ones are roasting.

I suppose if I just lower the TRVs downstairs once the place heats up, then more hot water will be available for rads upstairs? They're all on single zone.

To rebalance, could I open the LSV say a quarter turn on each rad upstairs? I have a tendency to make these things worse!:(