Hi there, we had some new radiators installed, but some of the valves are hissing on 2 of the radiators. For example, in the first floor bedroom (furthest away from the boiler), there is a hissing sound on the valves when they are nearly closed. This is true on the TRV (when the TRV is at some medium setting, for example 3, and the room is at about the right temperature, so the valve is just about to close). Setting the TRV slightly higher, or lower, solves it temporarily until the new temperature is reached. Having read some of the threads on this forum, I tried turning the lockshield down to decrease the flow through the radiator. However, if I turn the lockshield down enough, it hisses too. This solves the problem with the TRV, but there is no setting at which neither valve hisses. The other radiator for which this happens is on the ground floor, but also very far from the boiler. I don't know if this means anything. The boiler is a boiler with no settings for pump speed adjustments, and an internal bypass valve. The pressure is at the low end (~1 bar). Any suggestions? At first I thought it was the TRV itself, but we have the same model at other rads where there is no hissing. Also, the fact that the lockshield also hisses indicates to me that it's not any particular valve that's having problems, but the radiator? I've read that hissing can be solved by bypass valves. Does this indicate I need to change the settings on the bypass valve in the boiler? Thanks for any help you can provide!