hi people. i have a potterton performa 24 which is about 8 yrs old and has been ok except for needing new diaphragm and o ring. had inhibitor in system from new. yesterday it started to make a noise which is kind of like a high pitched grinding screeching noise. difficult to describe the noise exactly. bit like a lorry skidding after slamming on the brakes. if i turn down the temperature controls the noise goes away. the hot water works well and also the heating. no other noises. any ideas for what it may be and how much to fix it. thanks for any help guys javascript:emoticon('
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