Room Thermostat v Valve Thermostats

Bowness72 · 21 Jul 2008

Hi

I currently have thermostatic radiator valves on all but one of my radiators and am thinking about having a room thermostat installed because i was once told that it would be more efficient.
I have a vokera combi boiler on a timer but was told that the boiler would still be firing if the timer was set to the on position no matter what the valves were set to because the boiler had no way of knowing whether the valve thermostats had reached their set temperature.

Can anyone tell me if that is true ?

Thanks

D_Hailsham · 21 Jul 2008

Yes, what you have been told is true. The TRVs will shut the radiator off when the room reaches the temperature set on the TRV, but the boiler will continue cycling on and off.

When you fit the room stat you will need to either replace the TRV in that room by a lockshield valve or take the head off the TRV so it does not conflict with the room stat.

If you do not have the manual for your boiler, you can find it at Vokera Product Range

Click on your model then select Installation Manual

If you do not want to replace your timer, I suggest you get a Honeywell DT200 Thermostat. But, if you want to go the whole hog and get a programmer-thermostat, the Honeywell CM900 range are hard to beat.[/url]

Bowness72 · 21 Jul 2008

Do you think this inefficiency would be reduced significantly if a room stat was installed ? and is fitting a room stat a straight forward diy job or do you need to know something about the boiler ?
I am not sure if the current timer is a programmer or not. Basically I can set the time on and off for both the hot water or central heating separately and differently for each day with three time start and finish times.

D_Hailsham · 21 Jul 2008

Yes it is worth doing and will pay for itself in a very short time, paricularly with the threatened/promised hike in fuel prices.

Make and model of boiler and timer would be useful for advice about how easy it is to do

Why do you need to set on/off times for the Hot Water? With a combi, the hot water is heated instantaneously when you turn the tap on.

Bowness72 · 21 Jul 2008

Thanks. I assume the timer has the hot water option incase it was used on a different type of system. I will post further information on the boiler and timer.

superdupergasman · 21 Jul 2008

average saving for having an additional room stat is £65 per year approx, now as gas goes up so does the saving.

rssteve · 21 Jul 2008

could someone please explain to me how installing a stat with save money. From the way i see it you set all your TRV's and when all have got up to temp the bypass valve will kick in, the water coming out of the boiler will be going straight round and back in again, and not having time to cool down, the boiler will then shut down heating until one of the rad valves opens up calling for heat, the boiler will notice the drop in temp of return water and start up again.

If you then installed a stat say in your living room, and set it to the same as the rad valves. once this room gets up to temp it will shut the boiler down, but all the other rooms might still be calling for heat?

superdupergasman · 21 Jul 2008

Easy......no stat.....boiler runs ans runs for full time timer is on.....cycling on and off...pump running const.

Room stat...on for 1 hr maybe...up to temp...everthing shuts off...no energy used after this point until stat calls again.

rssteve · 21 Jul 2008

superdupergasman said:
Easy......no stat.....boiler runs ans runs for full time timer is on.....cycling on and off...pump running const.

Room stat...on for 1 hr maybe...up to temp...everthing shuts off...no energy used after this point until stat calls again.

yes that would be obvious less energy is used, but the point i am trying to make is the room with stat gets up to temp, boiler shuts down, but every other room might still be cold and calling for heat. And surely the boiler does not run constantly, if the return water comes back hot still i'd pursume it shuts down otherwise the water would boil? Im not disagreing i just want to understand it.

superdupergasman · 21 Jul 2008

If the system is designed properly, the rads are sized to the room thus heating them up to the required temp at the same time as the hallway with the room stat is heated to 20oC

D_Hailsham · 21 Jul 2008

rssteve said:
And surely the boiler does not run constantly, if the return water comes back hot still I'd presume it shuts down otherwise the water would boil? I'm not disagreeing i just want to understand it.

Yes the boiler will be shut down by the boiler thermostat but the pump will continue running and soon the water will have cooled down, so the boiler will ignite again, even if the TRVs are still closed. This will continue until the timer turn the system off.

superdupergasman said:
If the system is designed properly, the rads are sized to the room thus heating them up to the required temp at the same time as the hallway with the room stat is heated to 20oC

That is OK in theory, but how many systems are designed properly? The majority seem to be based on "experience" or guesswork or "think of a number" techniques.

rssteve said:
the point i am trying to make is the room with stat gets up to temp, boiler shuts down, but every other room might still be cold and calling for heat

Yes this can happen in badly "designed" systems. The solution is to put the room stat in the room which heats up the slowest or, if this is not possible, close down the valve (should not be a TRV) so the room does heat up slower than the others. It is also very important to balance the system if you have TRVs, otherwise they will not work properly.

Bowness72 · 22 Jul 2008

To be honest, I doubt that the system was "designed". It is an old house with half of the rads being cast iron and half normal. I have had problems with the balancing.

Bowness72 · 22 Jul 2008

The boiler is a Vokera Syntesi and the timer/programmer is a Drayton Lifestyle, if thats helps anyone tell me whether its a diy job to fit a room thermostat or not ?

JohnD · 22 Jul 2008

you can get a wiring diagram and instructions from the Invensys Drayton Controls website (or they will post you one as the online one is difficult to read or print) though they will need the model no (e.g. LP722) of your Lifestyle controller.
http://www.invensyscontrolseurope.c...TONLIFESTYLELPRANGE-ElectronicProgrammers.htm

then have a look at it and decide if you're up to it. It is very slightly easier if you use a Drayton thermostat like an RTS1 as it will be included in their diagram, but other makes are very similar.

D_Hailsham · 23 Jul 2008

Make sure that any thermostat or programmable thermostat you buy has volt free switching. Your boiler need this.

You can find the installation/service manual for your boiler at Vokera Manuals

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Room Thermostat v Valve Thermostats

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