Radiator causing confusion

Luckysasha

Had an issue with two rads in the house (bungalow) cold on the bottom lukewarm on the top. Everything seemed to point to sludge so I took both rads off today and flushed them out. Bit of sludge from both. Also opened the balancing and thermostat valves on the pipes while I had the rads off and ran the water. All looked good and clean. Put rads back on filled and bled them. Turned heating on and balanced all the rads in the house to 60 deg using a digital infrared thermometer. First rad I took off brilliant all is well with it. The second rad total disaster. Had the heating on for half an hour and it reached 34 deg. Both pipes where lukewarm at best at 21deg. Had a quick look under the floorboards and the pipe feeding the balancing side is copper with a white sheating but there seems to be some slack in it and it’s sagging about 8 inches. Could this have anything to do with my rad not heating.

Pete67

Most likely a balancing issue, unless you returned the lockshield valves to exactly their previous position. When balancing you need to measure the temperature drop across each radiator, and adjust the lockshield valves to get a 10 to 15 degree C difference between supply and return ( 10 degrees for conventional boiler, 15 degrees if you have a condensing boiler)

Remove the heads from all TRV's first, and fully open any manual radiator valves. Close all the lockshield valves fully, and then open approx 1 full turn. Turn any room stats up to max so the heating stays on while you are balancing. Leave the heating running for a while until temperatures stabilise, then measure the temperature drop across each radiator. If it's less than 10 degrees (15 for condensing boiler) the flowrate through the radiator is too high so close the lockshield slightly. If it's more than 10 (15) then there is insufficient flowrate so open the lockshield slightly. Allow temperatures to stabilise again and recheck the temperature drops. Repeat until all radiators are working correctly.

Proper balancing takes time and effort, and for this reason it is not always done correctly.

Luckysasha

Cheers Pete67. I was measuring around 8 deg difference on all the other rads except the offending one. I will give it another shot and see how I get on

Luckysasha

So balanced all the rads to 10 deg difference. Still can’t get heat in to the offending rad. It’s running at 40 deg at the top of the rad whilst all the others are sitting at 60 deg. It feels cooler at the bottom middle of the rad so I might flush it again

the_pen_turner

Turnoff one or two of the other rads and see what happens. If it helps then it's the burner or pump causing it

the_pen_turner

Turnoff one or two of the other rads and see what happens. If it helps then it's the burner or pump causing it

Pete67

What size is the copper supplying the rad? If it's 10mm it could well be blocked somewhere, especially if the heating system is suffering from sludge build up. Even 1/2 inch can get blocked if there is a low point where sludge can settle and build up.

Sludge is indicative of another problem somewhere, usually corrosion of the radiators from the inside, which occurs when a system is leaking and topping up with fresh water constantly. Could this be happening? Is the system sealed or open vented? Is there corrosion inhibitor in the system?

Also, if the system was recently drained you might have an airlock which is preventing proper flow to that particular radiator. Turn off all the other radiators, open that one fully (both sides) and run the pump. See if any air is pushed into the radiator where it can be vented off.

Good luck.

Luckysasha

The system was installed in 2010. Brand new everything except the boiler that was only 2 year old at the time. It’s a semi sealed system. It’s fed from the cold water tank in the attic via a non-return valve and there is an expansion vessel beside the boiler. The pipe is 1/2” copper. I tried all the other suggestions ie: turning off all the other rads, turning off the heating coil in the cylinder basically everything I could think of to force water through to the offending rad but nothing worked. That’s why I went down the road of flushing the rads and it worked for one of them but not the persistently cool rad !!! That’s why I was thinking there might be sludge caught in the sag of the pipe as this is the feed to the balancing side of the rad. My next step would be t9 lift the floorboards and take a temperature of the pipe run before and after the sag just to see if there is any difference

Luckysasha

So I took off the offending rad again today and flushed it out. No sludge of any kind came out so I put it back on the wall. Started again with balancing the system using Pete67 instructions. Had trouble getting the 10 deg difference on 2 of the rads so I balanced them as best I could going by there top temperature. Happy to report I managed to get an additional 10 deg in to the offending rad. So 7 rads are running at 57 deg and the offending one is now up to 50 deg. I didn’t want to push my luck trying to get anymore heat in to it as it took me the best part of 3 hours to get to this stage but worth it in the long run. Thanks to Pete67