Central Heating question

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Hi all,
I have been thinking about my central heating this morning as it seems to be getting very toasty at the moment. We have a Combi boiler (Worcester Bosch Highflow 400) which has a heat setting on it. There are TRV on all the rads (except the bathroom - I assume to stop the boiler overheating if the TRV's shut off) , but we dont have a room stat.
Are the TRV's really temperature controlled or do they simply reduce the amount of water the rad can get? If that is the case, then with no room stat, the only way I can control the overall temperature is by the boiler, so I have to go into the garage and turn it down/up. Is this a normal set up?
Normally I would leave the heating on 24*7 during the winter and control it via the room stat so it would get to a reasonable temp and then switch off, but now if I leave the heating on the boiler tuns all the time (this must be expensive!!) and the bathroom is like a sauna. The missus loves it, but I guess the heating bills will be huge!
Any thoughts?
Mike
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Mike Hibbert wrote:

bothered with the hassle of roomstat wiring...

models e.g. CM67 RF.
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Thanks Bill, it would still need wiring at the boiler end wouldn't it? Is that a (relatively) straightforward job?
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Mike Hibbert wrote:

Presumably you have a programmer with a time switch which tells the heating when to come on? There will be a cable connecting the CH ON terminal on the programmer to an appropriate point on the boiler. This cable needs to be diverted to go via the roomstat - so that the live feed only gets to the boiler when the programmer and roomstat are *both* calling for heating. In other words, the CH switch in the programmer and the roomstat both need to be wired in series between the mains and the boiler. You may well have a junction box somewhere to which the programmer and boiler are both connected. If so, this probably has a link between the two terminals to which the roomstat needs to be connected. If this is the case, you simply need to remove the link and take 2 wires to the stat - probably to the COM and NC terminals if there are more than 2. I assume that the pump is integral with the boiler - or at least controlled by the boiler? If so, this will take care of itself once you have the boiler under control.
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Hello,
I have just pulled out the wiring diagram for the boiler and it looks ok actually. I simply (!) need top wire in the live, switched live and neutral from the stat and then remove a link between the live and switched live points.
___ A / B-/\//\- C (room stat) | | | | | | 1 2 3 (control board) \___/
Where A is live B is switched live C is Neutral
and the link beween 1 & 2 is to be removed
Cheers for the advice!
Mike
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Mike Hibbert wrote:

Should be a piece of cake then! As others have suggested, If you use a wireless programmable stat you will need virtually no wiring and will also be able to have different temperatures (or switch off completely) at different times of day - even if you don't currently have a timeswitch in the system.
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On Sun, 07 Dec 2003 17:06:25 GMT, "Mike Hibbert"

Mike
I spotted a couple of things from your original post.
TRVs are fairly effective in that they do monitor the room temperature (albeit they are a little influenced by being near the radiator). There is a wax or equivalent capsule inside which expands with temperature and reduces and ultimately stops the water flow. In that sense they are somewhat more "analogue" than "digital" which is not a bad thing anyway. Of course, you also have the effect in a house that there is transfer of heat from room to room so the overall environment is quite complex. However, they are effective for what they are.
Adding a room thermostat is a good way to implement overall control of the house temperature.
I completely agree with Bill, an RF thermostat would probably be a good solution for you. Apart from the Honeywell CM67RF there is the Danfoss TP75-RF (about to be superceded by TP7000-RF)
These consist of a remote unit which you can site anywhere, or even take from room to room if you wanted. There is a clock and a temperature setting and measuring function and the whole thing is battery powered.
One useful capability is of night set back. This means that you can drop the temperature over night by a few degrees rather than turning off the heating completely. 6 degrees or so setback is fairly typical. Apart from the improved comfort, depending on the system and the house, doing this can also result in less use of energy as well. One of the principles behind this is that in some systems and houses, when the heating goes on in a cold house, there is an overshoot past the set point and more energy is used. If the house is not as cold then the overshoot is less. However this does all depend on the complete environment of the system and the house thermal characteristics. Also, with this type of room thermostat, the temperature sensing is more sensitive and accurate than an old fashioned bimetal strip type.
Moreover, there is also what is called a proportional control facility. This basically turns the boiler on and off in proportion to the heat required when the temperature is a degree or two either side of the set point. The effect is that overshoot can be practically eliminated.
Added to this, the boiler that you have is a modulating type which will adjust heat output according to demand. Overall, this sounds quite complex. In one sense it is - the control theory for a system like this and a house is involved.
However, you don't need to be overly concerned. The main points to achieve are that a) you are getting to the right temperatures when you want them, b) that there is not significant temperature overshoot when the system begins the start of a heating period and c) that the boiler doesn't short cycle (= 30-60 second burns) because it is producing too much heat. In reality, you have to experiment a little until you are happy with the settings.
Regarding installation, at the boiler end you have a receiver which is connected to the boiler. You can download the installation manual for the boiler and you will find a wiring diagram. The boiler has a set of terminals with a permanent live and a switched live for the heating. At present, these will have a link between them, I would expect.
After removing the link, you would wire out to the receiver (which should be located outside the case of the boiler) using the permanent live and neutral and then the switched live, plus an earth if required.
It's possible that you might already have a timeswitch on these two terminals, although I note that some versions of this boiler have one built in.
The best thing if there is a time switch already would be to set it to 24x7 as you are now and to use the clock function on the remote room controller.
If you can run the wiring easily, there are non-RF versions of these two programmers which cost a little less and have the same functionality.
I hope that that helps. This is not a particularly difficult task if you are comfortable with doing wiring. Obviously, sketch down what you have before you start in case you need to revert back for any reason.
.andy
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Mike Hibbert wrote:

Well, your system certainly wouldn't satisfy the latest building regs on energy efficiency - because the system has to be capable of turning itself off when the heating demand is met.
The simplest solution is to install a room stat - which really needs to be in a room whose radiator *doesn't* have a TRV - otherwise they will fight. You could probably put it in the hallway, and leave the TRV on that rad fully open - or, even better, swap it for the conventional valve on the bathroom rad.
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Set Square wrote:

The booer will turn itself off. It has its own stat on teh water temp.

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In an earlier contribution to this discussion,

boiler?

ISTR that you said something similar in an earlier thread. Whilst true, it still wouldn't satisfy the new regs because it will come on again when *it* cools down - even if no heating zones are calling for heat.
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Set Square wrote:

No, not when IT cools down, when the water circulating through it cools down, and if you have insulated pipes and no demand, that will be an awfully long time. In my case well over ten minutes to overcome the thermostat hysteresis. Then a quick minute burn up to temp, and a ten minute gap again.
In fact since I superlagged the CH pipes in the attic, its even longer now.

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So your boiler runs 10% of the time during the middle of the day when no heating is required?
This is simply not allowed for a new system. You might think it acceptable. HMG thinks not. If no heat is required, the boiler and water must be allowed to cool down. The requirement is pretty clearly worded (but only applies to gas/oil, not solid fuel).
Christian.
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Or reply to IMM as this loon thinks he is me.
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Yes, but it doesn't measure the room temp, on nights when it has been cold, I have to turn the boiler up or it gets cold, and then the next day the place is boiling so I have to turn it down again. A room stat would give consistency.
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Mike Hibbert wrote:

TRV's are room stats you burk!

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On Sun, 07 Dec 2003 19:59:08 +0000, The Natural Philosopher wrote:

have to do since this is not a new replacement.

with interlocks.
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Duh! Then it will cycle. The regs say it requires a control interlock. Which mean when all the house is satisfied the burner is off.
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writes

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Good question Maxie! Our snotty uni person is surrounded by them. He was banished from mixing with normal people.
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geoff wrote:

Dunno.
I actually don't run my central heating when the whole house is warm enough.
And teh boiler cycles in teh house stat when one is used anyway. So waht is the difference?
Nothing, except the pump runs all the time.
There is no requirement to make sure your pump doesn't run when the whole house is warm.
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