Upgrading controls


Postby jmf1 » Mon Dec 17, 2007 11:06 am

My CH system was installed about 28 years ago. I had the boiler replaced about 8 years ago, and have annual services carried out. I have had TRVs fitted to most radiators. The system is controlled by a rotary timer with two "on" and two "off" push-in settings. There are two rocker switches, one three position - timed-off-constant; and one two position - hot water and heating-hot water only. Sorry, don't have model details with me. There is one room thermostat, in the lounge.

My question is - can I replace the room thermostat and main programmer with a combination which will let me set my heating at a lower temperature overnight, or when I am away from the house for a few days, but revert to a higher temperature just before getting-up in the morning, or returning to the house after I have been away for a few days?

If that makes sense, I look forward to your replies!
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Postby htg engineer » Mon Dec 17, 2007 5:25 pm

No - the boiler thermostat ultimately determines the temperature, this can be adjusted for overnight and when you go away.

The room thermostat will only control the room it is fitted in, and the positioning of these have to be thought through - they're no good opposite windows as if the sun is on it - it will shut down the heating for the rest of the house which may still be cold - they're also no good above radiators.

The same with TRV's really they only control the radiator they're fitted too, so you could turn this down to 1 or 2 overnight and have it on 4 or 5 during the day etc.

I hope this makes sense - and hope it helps
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Postby robertw63 » Tue Dec 18, 2007 12:03 pm

I don't agree with this answer. You can indeed do what you say (my house is set up like this) within limits.

Your present system isn't 'perfect' anyway because when the lounge thermostat is satisfied the heating will go off whether any of the TRV-controlled radiators is satisfied or not. However that is what you've got so .....

Just do as you suggest. You can get programmable lounge thermostats which you can set to different temperatures at different times. When the lounge wants a lower temperature the boiler will go off earlier and some of the other rooms will likely be colder than you prefer but it will work more or less as you want.
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Postby robertw63 » Tue Dec 18, 2007 12:05 pm

Oops!!! And I should have said that you don't really need to change the programmer to do this. You can get room thermostats which can be programmed for different temperatures at different times of day or even as you mention for holiday periods etc.
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Postby jmf1 » Tue Dec 18, 2007 2:57 pm

Thanks guys, I have gone ahead an installed a honeywell CM907. However, I am already getting problems with temperature control.

Can anyone with a CM907 explain, in simple terms, the operation of the time periods? Honeywell tell me that periods 1,3, & 5 are period starts and 2,4 & 6 are period ends. I am confused, since I do not see this represented in the user manual!
:?
During this cold weather, I want to run the system 24/7. If I want the temperature to be kept at 16C between 0300-0600; 20C between 0600-0900; 16C between 0900-1500; 20C between 1500-2200 and 16C between 2200-0300, how do I set the temperatures within the time periods?

If I set 1-0300/16; 2-0600/20; 3-0900/16; 4-1500/20; 5-2200/16; 6 disabled, will this result in the temperature control I require?

Thanks
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Postby htg engineer » Tue Dec 18, 2007 9:19 pm

robertw63, what's a lounge thermostat ?
This installation will have a room thermostat, which can be fitted in any room - not just the lounge.

If the lounge has a gas fire then the room stat shouldn't be in there anyway.

The room thermostat should not be in the warmest or coolest part of the house. As if it's in the warmest it will cut the pump off before the rest of the house is heated. If it's in the coldest part of the house, the rest of the house could be hot, and the heating would still cycle on and off (not energy efficient)

If the room thermostat is located in the correct place, then yes your TRV's would control the temperature of individual rooms, and they could be set at different temperatures.

If you fit a programmable room stat in a room with a fire (not sure if yours has a fire) when the fire is on it will cut the heating off and the rest of the house will still be cold.
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Postby robertw63 » Wed Dec 19, 2007 8:14 am

Yes of course it will htg engineer, but the original question was whether the (already fitted) thermostat (which is fitted in the LOUNGE ie it is the LOUNGE thermostat) could be altered to a programmable one. Of course it can. Your comments about the other TRVs etc. are correct enough but none of the control effects change just because the thermostat has become set to a different temperature.
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Postby jmf1 » Wed Dec 19, 2007 8:34 am

Htg engineer, thanks for your reply, but I think you misunderstood my question, I am familiar with the operation of TRVs at room level. I wanted the system to operate at different temperatures during the 24 hours, and not be constrained to the one temperature set at the thermostat. The CM907 will do this, when I get used to how it operates, including whether I dare use "optimum start"! I appreciate that, because the thermostat is in the lounge, I will have to be careful not to let this room get too hot, and yes, it does have an open fire!

I think you will find that robert referred to it as a "lounge" thermostat, because that is where I said it was situated!
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