New Central Heating timer Help

[Mart Rhodes]

Hi Guys, My central heating timer is playing up, its a old mechanical clock type with little pegs to set the On/Off time, make unkown at this moment. I need some advice on fitting a new digital type timer. It only needs to control the Central Heating but most timers seem to do both CH and HW, would one of these be OK. I think there are 3 mains cables going to the exsiting timer (possibly one for theromstat, one for the boiler/pump and the mains supply?) although I'm just guessing! Can anyone advice a model or explain how to wire a new one up. I can post more info on my old model when I get home if this helps.

thanks in advance

[Christian McArdle]

Personally, I would replace it with a light switch. Then replace your room thermostat (or add if not already existing) with a programmable type. There are significant advantages to doing so. The advantages of a programmable thermostat are:

1. Usually in a more convenient location for programming/override.
2. Enables setback temperatures, so nighttime could be set at 10C, rather than -273C.
3. Enables thermostat logic to predict the length of time to warm up and so turn on early on cold days.
4. Prettier.
5. Similar cost.
6. Clock/digital temperature display.

Christian.

[BigWallop]

And could most likely be used with existing wiring you have, without any modifications, extensions or additions.

[Mart Rhodes]

Hi Christian, Never thought of that option, now if I understand, could I just leave the original fulty time just left on constant and control the "new on/off timer" with a programable thermostat? I can see what you mean about just change the old one for a switch but don't really understand the wiring for that. Is it a case of the supply is just swtching the pump and new thermostat on or off? Thanks again, meanwhile I'll do a search on a programable thermostat.

[Christian McArdle]

If the existing one is working to the extent of having a working "always on" mode, then indeed there is no need to replace with a switch.

Christian.

[Mart Rhodes]

The old timer has just been left on constant and we "turn on/off" the heating when we get in by the thermostat. Thats fine but now its getting cold I needed to replace the not working timer, anyway I think I've found a programmable thermostat and its about £30

This looks like what I need.

thanks for you help and a good suggestion, I didn't know these things exsisted!

[Christian McArdle]

There's a whole world of these devices out there. You might want to shop around to find one with facilities and appearance that suit your decor, rather than necessarily buying the first one.

Christian.

[P.R.Brady]

Will you also want to run domestic hot water heating on a timer too? In that case, a timer/room thermostat alone won't do the job. Phil.

[Lurch]

On Thu, 25 Nov 2004 17:54:27 +0000, "P.R.Brady" strung together this:

[Mart Rhodes]

There is too many to choose so I'll go with my insticts and get that one, should be here today and I'll have a gone at fitting it tomorrow. thanks for your advice and I'll let you know if 'm successful!

[Christian McArdle]

Note that the existing wiring probably has 3 wires. There is usually a live input (only when the CH is turned on at the programmer), switched live output and a neutral. Electronic thermostats do not require the neutral connection.

This wire should be safely terminated and insulated. The live input goes to 'C' and the switched live output goes to 'NO' or 'NC' depending on whether the manufacturer considers the normal temperature to be lower or higher than the setpoint. I think 'NO' would be more common.

Christian.

[Mart Rhodes]

Well, its arrived and looking at all the various diagrams with it, I'm not sure! Basically it has 4 connections: 1-Line, 2-Load Heat, 3-Load Cool, 4-N parking. So am I correct in thinking just using 2 wires on the exsisting thermostat (which two as yet I don't know) are connected to connections 1 and 2? I realise its hard for you to answer when I don't even know what wires are to the exsisting thermostat, but when I get into it, it may all become clear!

Thanks again for your help

[Christian McArdle]

Put the "permanent" live to '1-line'. Put the switched live to '2-load heat'. Any spare neutral goes to '4-N parking'. They've been nice enough to provide a terminal to stick the unwanted neutral on. Nothing goes to '3-load cooling' unless you've got air conditioning, you b*stard!

If you've only got 2 conductors to deal with, stick them on '1' and '2' at random. It is only if you've got 3 wires that you have to worry about identifying which one is neutral.

Christian.

[Mart Rhodes]

Installed fine, no problems, using pins 1 and 2, neutral on pin 4. Thanks for your advice, I'm really pleased, heating on when I get up and when I get home!

cheers