high pitched squeeling valve

[taxi]

Am I really the first radiator related forum post since 2007? Anyway, hope someone out there can help.

I've tried bleeding the radiators and tightening the valve itself to no avail.

There is a high pitched squeel coming from my son's bedroom TRV when it is on a setting at 3 or under - usually in the early hours! Trouble is at 3.5 it's just a bit too hot, even with the boilder setting reduced, and at 2-3 it squeels, and below 2 no hot water at all seems to come through.

My bedroom one is similar, but not quite as bad. There's no water leaking, just this sound - and at 1/2 am uit's a nigthmare. Help!!

 

[polesapart]

sounds like an unidirectional TRV installed on the return. Check if there is an arrow embossed into the valve body. is it one way or with two arrowheads? the flow pipe is the one that gets hot first when you turn on CH with TRV open.
If unidirectional TRV on return i.e.allowing flow against the flow direction indicated by arrow you will get the symptom described. solution is to fit a bi_directional valve or swap the rad valves over. Most, if not all, new TRvs are bi.