Don't know but ensure to flush out the system repeatedly as there are some horror stories of gases being generated due to lack of proper flushing after a chemical clean.Not yet, I went out to get some cleaner from toolstation this afternoon. The diverter valve was fully cleaned before I put it into the system, so the scale has come from other pipework, I suspect the bit I found would not by itself have caused this problem, but it does tell me scale has built up elsewhere. So I will circulate some cleaner around the pipes for a bit and see if it starts behaving.
Does a Vaillant have any aluminium in it? some of the cleaners have to be washed out after only 3 hours if there is.
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