1 radiator cold on single pipe system

[John Bragg]

The single pipe system comprises 4 downstairs radiators and 7 upstairs. It has worked fine in previous years and all radiators have heated up. It has been dormant all summer and now when kicked into life all the radiators heat up except one. I have removed and flushed out the radiator (very little sludge) and run lots of water out of the 2 tails. This is slightly coloured but nothing too abnormal. This had no effect. I then ran the rad on its own with all the other 10 turned off. The inlet tail got hot but the rad remained cold. I then turned on the upstairs rads and, hey presto, the rad got warm but not exactly hot. Thinking I was on the home straight I then turned on the 4 rads downstairs. This caused the troublesome rad to go completely cold again, so back to square one. I have solicited advice on this problem and have been advised to put in a chemical flush, change the pump, and even told that the system could never have worked because the rad in question is a modern rad while all the others are old flat panel ones. However it HAS worked fine in the past. Also I have been told that the flow is both too low and too high. HELP!!

 

[John Bragg]

I had no replies on this problem but I thought I would update the thread to say it is now fixed. It has taken some 4 weeks. It has involved 2 periods of chemical flush with Sentinel X400 and changing the pump. Even this didn't fix it completely and the system was obviously generating its own gas, which I assume was hydrogen, and this was accumulating in the input of the troublesome radiator and preventing any flow through it. I have finally cured this by repeatedly bleeding the radiator over a 2 week period with only the input valve open and adding 2 litres of 4Trade inhibitor. The system now seems to be free of gas and working nicely. So I guess that the system was pretty blocked up and corroded with the corrosive reaction generating gas and causing an airlock in the highest part of the pipework. Frankly I could do without all this sort of hassle and the plan is to heat the house by keeping the multi-fuel stove going all the time. This works a treat and looks nice!!

 

[GrahamM]

Missed you first post. Glad you got it sorted. The old sludge bites again!
Thanks for the update.