Identifying common wire from boiler

Hi,

I'm just replacing my old thermostat and programmer with a Hive active heating one. The previous thermostat and programmer had wires running into another room where they were displayed and I'm planning to fix the receiver unit much closer to the boiler. As such, its not a straight swap out and I wondered how I can determine which is the common wire and which is the heating on wire as they're both black wires....

Really appreciate the advice. Thank you!

follow them back to where they start then a continuity test will tall you which one is which

Ok thanks, in that case I'll need to track it into the boiler. If I were to connect the wires incorrectly, i.e the common wire to the heating on port and the heating on to the common wire port, would this damage anything or would it simply not work?

potentially ramming 230v into something thats not supposed to have 230v could well do some damage

I've tracked it back and one of the black wires eventually connects to the blue wire housed within the same original group of wires. Would this make it the common wire?

no idea. youll need to read the manual / wiring diagram for whatever boiler you have

I see, thanks. Would there be an alternative way to identify the common wire i.e. is there a safe test that can be done to see if the wire carries 230V or not? Thanks

yes. stick your finger on the end. if nothing happens its not the live. if you end up thrown accross the room / dead then its live.

or you could try using a voltage tester / multimeter...

Stellar advice thanks. Sure this would be a simpler approach that tracking the wiring back and reading the manual for the boiler. So the common wire will carry 230v while the heating on wire will be carrying no voltage?

Bridge20 said:

Stellar advice thanks. Sure this would be a simpler approach that tracking the wiring back and reading the manual for the boiler. So the common wire will carry 230v while the heating on wire will be carrying no voltage?

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probably. different boilers work in different ways though. sometimes its voltage free. you will need to read the manual & wiring diagrams for your boiler to find out. get it wrong and something may go bang, and you may need a new boiler to go with the hive. but what the hell, just wing it and take a guess throwing in connections where you think they go

It might help us to help you if you tell us which boiler you have 

It could even be a low voltage control circuit, normally 24 volts, either way you need to know what you are doing, or potentially saving around 50 quid for someone to wire it could cost a lot more, the last circuit board I replaced was £90, and that was without my charge for fitting it!

No idea. You will need to read the manual / wiring diagram for whatever boiler you have

Switching thermostat by manually deprived of a Denver HVAC specialist can be pretty disturbing if you do not hook up the wiring appropriately. Inside of the thermostat there are numerous terminals which need hook up with the correct wires. The R-terminal is the thermostat's power. R means Red, the repairman must need red wires going to this terminal. This control arises from the transformer. The transformer is generally in the editing unit or the air handler in a split system. Since they are supplying power, it is a decent idea to kill the power to both the condenser and the air handler earlier working on the thermostat.

He's been waiting 2 years for that reply.

ProDave said:

He's been waiting 2 years for that reply.

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And quite possibly a cold two years...