New 1800 x 700mm Radiator fitted hot at top cool at bottom all over

moray · Feb 11, 2010

I have had two radiators removed in my living room, one was removed and pipes capped off under floor to free up a wall. The other one was replaced by a larger radiator 1800 x 700mm Stelrad K2 Softline. I also have a Danfoss RAS-D2 TRV with bi directional flow fitted which also came with lockshield valve. All radiators in the house are fed with 10 mm pipe, this does not appear to be an issue as I have a fairly large radiator in kitchen which gets red hot also (1000 x 600mm). All radiators are red hot in the house apart from new one fitted. It is hot at the top 1/3 and getting cooler towards bottom 2/3'rds. The flow pipe is approx 68c and the return pipe is very much cooler at 42c. The TRV is fully opened and set to correct flow direction and pin moves freely. The lockshield valve is fully open have tried in other positioned from part open to half and no difference. The plumber completed drained system at outside drain cock prior to working on it and recharged when all was fitted. I have gone around and bled all radiators, I drained two bucket fulls from new radiator as well. The system in the house is fairly well balanced as I went around and checked flow and return temps on all other radiators. Any suggestions to what it might be, plumber is coming back next week to by pass radiator by connecting a pipe to flow and return to check for good flow to rule out radiator issue. The water in the system appears clean, plumber suspects new radiator may be at fault, is that possible? I called raidator supplier and they state they have never had a new faulty radiator due to bad flow! I have a worcester bosch 240 combi boiler. I am assuming its a blocked radiator or return pipe from symptoms, the two radiators I replaced worked great.

Alanka · Feb 12, 2010

Hmmm.... A quick test is to shut off all other rads in the house but leave the cool one fully open. Then, the full pressure of the pump is concentrated on that. If there are any airlocks or blockages they might well be cleared by this treatment and your problem will go.

However, you might find that though the cool rad now gets nice and hot, it goes back to cool again when you re-open up the rest of the rads. If so, it would mean that despite what you say, the system needs rebalancing.

If this test has no effect at all on the cool rad, then you really do have a stubborn blockage, I'm afraid. Was the new rad flushed out in the garden to clear any swarf or other manufacturing debris? It should have been! Are the valves clogged up?

Oh yes, air may be emerging from the capped-off doglegs, which could cause airlocks.

moray · Feb 12, 2010

Thanks for reply Al, I did shut all of apart from small bathroom one whicch has no TRV. I may shut that of tomorrow with spanner and try again but the rad stayed same so I dont think balancing. More like an airlock or blockage 🙁 The plumber never flushed the rad he just fitted it as I was there when he did it. The heat distribution is very even, top 1/3 hot and 2/3 coller then last 3rd cooler again. The end with flow is hot all the way from top to bottom for first inch or two in. return pipe cool. What would be the next course of action if it was your rad? Are the rads not tested at factory by filling with water, I guess not