Low voltage room thermostat.
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Low voltage room thermostat.

by Paul-E » Sun Jan 04, 2009 6:05 pm

I have had a combi boiler installed for quite a while now and for ages now I've controlled the temp for central heating by the thermostat on boiler. However I think it is about time I put in the room stat.The problem I have is that the cable going to the old stat is 1.5mm (old stat on old boiler was 240v) and the new stat is low voltage........will the 1.5mm cable be ok to use or do I have to run a new cable which will be a nightmare due to position of boiler. Don't want hassle/cost of fitting individual thermostatic vales. Any advice appreciated.



by ericmark » Mon Jan 05, 2009 1:12 am

If you look for example at http://www.screwfix.com/prods/17585/Plu ... Thermostat these have volt free contacts and are battery operated a pair of AA cells will last around two years and easy to change. This is not only a thermostat but also a timer and instead as with old idea of switching on and off it switches between temperature setting.
It will work with your existing cable. I give one example there are many more. I use this one myself and there is one point I don't like it has the same settings for Mon to Fri with 4 separate temperatures being selectable but Sat and Sun are separate with only 2 setting for each day.
The temp can easy be changed and reverts back to program at next program change. Before I had a simple temperature only electronic thermostat very little price difference batteries lasted longer and both had a 0.5 degree between on and off. Before that was old mechanical type with neutral connected these had about 1 degree between on and off and without neutral connected about 2 degrees between on and off and at that you really felt the chill before it cut in again.
The battery operated units today are normally designed for both heating and cooling so have a com plus on normally open and one normally closed contact for heating com and N/O only are used on the one I have but instructions that come with it are good if a little small in size.

Posts: 59
Joined: Mon Jan 05, 2009 4:47 pm

Thermostat installation

by singer » Mon Jan 05, 2009 5:45 pm

I think what Ericmark is refering to is a programmable thermostat which runs on its own batteries. There are dozens of different ones on the market, including wire free transmit/receive versions which are a doddle to fit. I suggest you go to ebay to source these as there is a massive choice at low prices.
The use of these devices means that in effect the central heating is never off, instead you simply program a temperature to a time zone and the boiler maintains that temperature. For example if you program in 22 degrees at 7am, 15 degrees at 10am, 22 degrees at 5pm and 15 degrees at 11pm the boiler will at 8am bring the house temperature up to 22 degrees until 10am then maintains the temperature at 15 degrees until 5pm etc etc which means that if you get a sharp frost overnight or during the day when you're out at work the stat will always switch the boiler on to compensate - very clever and a big improvement on older methods.
A few points to consider though - this stat replaces the clock so make sure the clock is either removed, disconnected or permanently switched off so only the stat controls the boiler! Also you say the old stat was 240volt. Usually the connections on the boiler to this type of stat are low voltage so make sure you're using the right ones. Better still buy the wire free version and ditch the existing wires altogether - then you can choose exactly where you install the stat if the old stat position is not quite right.
Hope this helps.

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