Hi Hurricane,
I think first of all you should calculate how big your radiators should be. I use an online calculator at Best Heating (
BTU Calculator | Radiator Sizing Guide - BestHeating »»). Then measure the size of your rads and compare them to something similar to get an idea of what output they have.
If your rads are undersized, the boiler will run and run and never get the place hot. Its not too good for the boiler either.
It sounds like you may need to balance your radiators to push the flow to the one in your bedroom.
Yes, it is right to put radiators under the windows. It can be a problem if you have long curtains hanging over the radiator.
Regarding thermostat positioning. I think the hallway is probably the best place for it but if the hall never gets warm enough to activate the stat then the boiler will never switch off. Does the radiator in your hall have a TRV? Because it shouldn't. The way a heating system should work is the room where the stats is should be the last one to get to temperature and the first to lose its temperature. That is why the hallway is good. So if you over heat your hall the stat will shut the boiler off too early and if it never gets warm enough it will never shut off.
This is why balancing the radiators is so important.
Have a go at balancing them yourself. It's not difficult.
Switch you heating on and off a few times and walk around and feel your rads to see what ones heat up first and get an idea what ones are the most served and which ones are the least served (the index).
You then need to leave your index radiator (presumably your bedroom) fully open and close all other to about 1/2 a turn open.
Yes 1/2 a turn. Radiator lockshield valves (the one without the thermostatic head) go through about 4 turns from open to closed, but all of the regulation (valve authority) is on that last turn. So 1/2 a turn open is a good place to start if you already now where your index is.
If you already know that this radiator is undersized, don't try to balance to it. You will just sacrifice the rest of the system for no benefit. Balance to the next coolest rad instead and get that one changed or repaired.
You said that you shut off all the rads except the one in your bedroom? When you did this did the bedroom get up to temperature?
I don't like the sound of your TRV being noisy. See if you can work out what make and model it is and check to see if its bi-directional or not. If it isn't, has it been installed in the wrong direction?
Check that the pin is moving. The pin is on the valve, the bit inside the thermostatic head that you referred to, presses the pin down. With the head off, press the pin on the valve up and down to check that it isn't stuck down. You can try pulling it up with a pair of pliars if it appears to be jammed but take care, I've heard of people pulling that pin out quite easily. You only trying to test if there's movement on it. If there isn't leave it and get it replaced.
Next, is the system dirty? You can get someone round to check this for you, but in my experience, flushing companies are usually more than happy to tell you it needs to be flush whether it does or not.
If your rads are sludged up you may find that they are cold along the bottom and around the centre. Have a look at some rad flushing company websites, they will probably have some pictures to show you where sludge builds up.
I've seen british gas engineers determine if the pipework is dirty by placing a magnet onto the copper pipework. The idea is that if the magnet sticks then there is sludge in the system. DON'T DO THIS or let anyone else do this. When you do this you will magnetise the sludge and turn a partially blocked pipe into a fully blocked pipe.
Let me know how you get on with these checks and we will try to narrow down the problems. I am happy to write a report on the system for you to submit to the council.
I hope this is of some help.