Combi Boiler - thermostat install questions

[ickleric]

Hi,

I have just bought a Drayton RTS8 Combi-stat thermostat for my Baxi 105HE combi boiler. It says that i should use a 3 wire connection. Now when i look at the manual for the boiler, i can see two connections which can be used for an external control. I'm not too sure what the 3rd wire is from. Any body know?

Also what sort of cable should i use to connect this thermostat to the boiler?

Cheers in advance.

 

[gas4you]

3 wires will be live in from boiler, switched live back to boiler and neutral for the anticipator to work I would think.

Just make 100% certain boiler will take 240V external controls. I cannot remember with this one offhand.

 

[ickleric]

whats the anticipator?

also whats the best cable? 2.5mm or 1mm?

 

[breezer]

anticiaptor is usually a resistor

it is connected across live and neutral and gets hot, its to make the bi-metal strip (that is the actual "sensor" ) move earlier, since it needs a fair bit of heat to move in the first place.

cable should be 3 core and earth 1mm is fine, remember to use coloured sleaving to indicate what colour does what.

But as said it depends on what your stat needs. (live, switched live or live, switched live, neutral (and earth)

years ago all room stats needed live neutral and switched live (and earth) but more modern ones only require live and switched live (and earth)

 

[Taylortwocities]

The description of that stat says

"Suitable for 2 or 3 wire combination boilers"

so you should be able to wire it up with just the two wires.

This may sound obvious, but didn't the stat (and the boiler) come with a useful piece of paper called

"INSTALLATION INSTRUCTIONS" ???

 

[ickleric]

Yeah it comes with instructions, it basically says that for Baxi they recommend for optimal performance to use 3 wires. So you think i only need to do the 2?

See below for copy of thermostat instructions & baxi instructions.

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• ickleric
• 17 Jan 2009
• 1

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• ickleric
• 17 Jan 2009
• 1

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• ickleric
• 17 Jan 2009
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[Taylortwocities]

Its pretty simple.

The recommendation is for you to run it as a 3 wire system. To do this you'll need 3 core and earth cable from the boiler to the stat.
Wire it s figure 5. The neutral wil be from the N connection in the boiler
Connect L from the stat to terminal 1 on the boiler and the connection shown as Load (terminal 3 on the stat) to terminal 2 on the boiler.

If there is a link between 1 & 2 on the boiler, remove it!

If you do not have three wires to the stat and/or its too difficult to run 3 wires then you can run the stat as a two wire system but you must follow the instructions relating to figure 6, otherwise the anticipator wont work properly.
Note, in this mode, the wire to terminal 2 on the boiler goes to terminal 2 on the stat, not 3.

 

[ickleric]

now i do have a basic 24hr timer which is on the main board, does this change anything?

also on the instructions it says to test L & 2 to see if the amps is below or above 0.6A with a multimeter. is says if below do figure 6 and if above do figure 7. Is there a way to know which one to do without multimeter?

 

[Click-Sure]

Yep, the controls on that boiler are 230v, the same as the duo-tec's controls.

 

[Taylortwocities]

You need a meter that can read amps. If you ignore the instructions then your stat will give you the wrong results which can mean

higher than expected bills
or (worse)
a significant other constantly complaining that the house is too hot/too cold

Maplin sell multimeters at less than £7 and had a buy one, get one free offer!