In terms of causing damage, probably nothing.
However the purpose of a cleaner is to put the scale, sludge and whatever else into suspension, so that it can be flushed out with the water. Leaving that filthy water in there isn't going to achieve anything in terms of cleaning.
Thanks for the reply Flameport.
I flushed the system earlier in the year with Fernox, after the system seemed to be slow heating up.
I flushed the Fernox out of the system from three different points on the system under pressure for about 40 mins from each point, until the water ran clear.
However, since then the system has become slow to heat up the furthest radiators away and I've thus put fernox in again and it has again done the trick, but I just wondered if leaving it in for longer would be a good idea ?
There is a Magna Clean on the system.
The problem is reprecipitation. The sludge will settle again.
Best to continue flushing until it's all gone.
Check the pump impeller for blockages too.
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