I had two single radiators changed to double last week and the boiler keeps going off and showing L-F alternating. Followed manual instructions and a lot of black deposit came out and I removed the very hard calcified stuff in the trap. Fault still recurring occasionally. Any suggestions as the plumbers are all away till next Tuesday? It is an Icos HE15 boiler.
Sounds as if you need some system cleaner, most diy places will do it, you put in the system, one way, is close off a radiator, partly drain it, maybe by undoing a valve connection to the radiator, drain just over 1 ltr out, as that is the amount you will get in a bottle, take off the plug on one end of radiator, use a funnel or something to pour the cleaner in. reseal radiator, reopen valves follow the instructions on the bottle, That will clean your system. You will then need to flush it out, and from what you say, I would advise then adding an anti corrosive to the system, would be next to the flush at the diy place. That would keep the system clean, to avoid the same happening again.
SD
December 2011
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