Thermostatic Radiator Valves

[opinion8]

I have some questions.
It seems that over the summer the function in all my Thermostatic Radiator Valves has atrophied. To start with they all seemed to be acting as simple on/off switches, but not reacting to the changes in room temperature at all. This now seems to have deteriorated to the point where all the radiators are on all the time. This makes the rooms uncomfortably warm, and ramps up the running costs of the system. So I need to do something (masterly inactivity would have been my preferred option).
First step is to go round with a hammer and a pair of pliers to make sure that all the spiky uppy downy bits do still move. Those I have looked at so far do seem to, but there are bedrooms with hungover offspring I can't get to at the moment. So my conclusion is that it is probably the thermostatic part of the valve that has failed and no longer opens and closes the valve.
The easiest thing to do would just be to buy straightforward replacements - I think what I have are ACL Drayton RT212s The characters ACL and Lifestyle appear on the plastic bit, but I can't find RT212 anywhere. The entire valve would cost £8.99 each - though I only need the thermostatic bit.
Question1 : could I buy just the thermostatic bit?
However there do seem to be options which might result in
a) a more pleasant home environment
b) reduced running costs.
For instance Housetech Intelligent Solutions sell a system which puts a trv on each radiator, controlled by a room sensor. Potentially it could link back to the boiler to switch that off if all radiators were in warm rooms. It is hard to disagree with their assertion "TRVs are attached to the radiator so they are measuring air temperature at the hottest point which is inaccurate. In our opinion the worst place to measure temperature" They claim savings of 25% and payback period of 18 months. I reckon that if I were to buy one Wireless Room Thermostat and 4 Valve motors I could control all four bedrooms (with a compromise on the room by room temperature control) for an outlay of about £200. I don't believe I'd get my money back in 18 months but it would be part of a gradual reduction in cost and increase in comfort.
Question 2: has anyone bought this kit from this supplier and can make comments on it?
Now there are still other options (wouldn't life be easier if there weren't?).
For example, on sale at the moment are Pegler Terrier I-Temp i30 Vertical Programmable TRV Now at £23.40 each the experiment with these for my four bedrooms would cost about £100. Advantages would be that each room would have a programmable thermostat - so bedrooms could be set to come on not too long before bedtime. Disadvantages over the Housetech solution would be that the valves are not motorised (I guess a motor is better than a simple expansion and contraction?) and we are back to sensing temperature at the worst point in the room,and there would be no weekly activation to keep things moving.
Question 3: Can anyone recommend the Pegler programmable?
Another option is the Myson 2m Remote Sensing TRV but I think I don't fancy this. For almost as much money as a Pegler all I achieve is moving the sensor, in return for which I get an irritating bit of wire.
Question 4 : Have I missed something about the Myson Remote?
Which of course brings me to the most important question of all
Question 5: What have I missed - is there someone out there who actually knows what she's talking about and can point me in the right direction?

[jwxfs]

You pay your money and take your choice.

The housetech type solution (I personally went for the Honeywell Evotouch instead) claim to save up to 30% in fuel bills as they switch the heating on and off according to the demand from each radiator. They therefore act as multi-zone systems allowing complete flexibility throughout the home. They are best suited to large systems where the four figure outlay is likely to pay back after 3 to 5 years (better than leaving the cash in the bank at an interest rate below inflation!). My fuel bill is currently 20% lower this autumn albeit we have not had last years severe weather. The real upside is that a single room can be brought up to a requested temperature very quickly and you have almost an infinite amount of flexibility.

TRV's including the terrier only control the radiators and therefore do not switch the heating off when all zones are up to temperature and therefore energy can still be wasted by the boiler running.

[opinion8]

You pay your money and take your choice.

The housetech type solution (I personally went for the Honeywell Evotouch instead) claim to save up to 30% in fuel bills as they switch the heating on and off according to the demand from each radiator. They therefore act as multi-zone systems allowing complete flexibility throughout the home. They are best suited to large systems where the four figure outlay is likely to pay back after 3 to 5 years (better than leaving the cash in the bank at an interest rate below inflation!). My fuel bill is currently 20% lower this autumn albeit we have not had last years severe weather. The real upside is that a single room can be brought up to a requested temperature very quickly and you have almost an infinite amount of flexibility.

TRV's including the terrier only control the radiators and therefore do not switch the heating off when all zones are up to temperature and therefore energy can still be wasted by the boiler running.

Thanks jwxfs for taking the time to respond. As you say a simple comparison between this year and last is confounded by the very different weather - my direct debit gas account is substantially in credit (nearly £400 - even more than at the end of the last quarter) even though all my trvs are defective! EDF (my supplier) "upgraded" its computer systems - an "upgrade" which means I no longer have access to last years online bills, making it difficult to do a comparison.
I found the Honeywell website an odd mixture - on the one hand they expect me to be taken in by the happy children and smiley parents in the wonderfully heated homes in their video, on the other they also expect me to know what a BDR91 is and what function it performs in the overall scheme of things. Even with your encouragement Honeywell have not persuaded me to look any further.

[jwxfs]

The Evotouch application manual http://products.ecc.emea.honeywell.c...c928g1000.html here gives a great overview of the system and the components. But as implied earlier it is only worth it for large systems that have no zoning built in.

If you do not want boiler switching, you are probably best going for the terrier's as you will get individual control of each room. As long as they are not boxed in by furniture etc they should be fine and give accurate temperature control. Just set them a couple of degrees lower than the ideal room temperature as the heat differential between floor level and head height can be significant if there are any draughts.