Help! No heating - thermostat wiring! CM927

[MJN]

Ignore the mains tester results entirely. At best they are misleading (and downright dangerous in every other respect).

Measure the voltages against earth as a reference with the stat disconnected. This way you can identify which wire is the permanent live and go from there.

Mathew

 

[benseb]

Here we go, with thermostat disconnected, measuring at the thermostat end of the cable...

E > Black = 0v
E > Brown = 235v
E > Grey = 15v

So looks like Brown is definately the permanent live. Grey is neutral (should there be a voltage difference here?)

Ben

 

[MJN]

The voltage on the neutral wire can easily float to such a figure as a result of various causes such as capacitative inductance from other (live) wires and a high-impedence multimeter is very sensitive to it. If you were to connect a load (e.g. light bulb) across L/N the voltage on the neutral would (should) drop to zero.

Given that your old stat controlled the boiler with the grey wire disconnected then you can now conclude for certain that with the brown being the permanent live then black is the switched live. The grey wire is therefore the neutral or, perhaps, not connected to anything at all. If it is the latter then that would explain why your receiver won't even power up given the lack of the neutral (compared with your existing stat which would benefit from it but didn't absolutely require it).

Mathew

 

[benseb]

Cheers.

It sounds then like the neutral isn't connected to anything. That's why the new thermostat half worked when I had the N and S/L swapped around - I presume it was pulling current from the boiler switch circuit.

But when it's wired up properly, if the neutral isn't connected it's not powering up the thermostat.

I'll see if I can yank the boiler out over the weekend - if there wire is in there hopefully it shouldn't be too hard to sort. Where should the neutral be wired to - the boiler neutral supply?

Ben

 

[MJN]

I'll see if I can yank the boiler out over the weekend - if there wire is in there hopefully it shouldn't be too hard to sort. Where should the neutral be wired to - the boiler neutral supply?

I'm just a DIYer and so I haven't seen all that many boilers, however of all the ones I have seen at this level of detail the neutral has been provided alongside the live and switched live terminals.

Mathew

 

[MJN]

Looking at the installation instructions the neutral for the stat should be connected to the supply neutral on the terminal block shown in fig 43 (pg 31).

Mathew

 

[benseb]

Nice one, I'll check it. Just got to try and get access to the boiler first as some numpty has been a bit over zealous when boxing in!

 

[MJN]

If it helps maintain your sanity try and view the current task of sorting out access to it whilst your boiler is at least working as being infinitely preferable to trying to do so when it isn't... You/someone will need access one day so you might as well sort it now.

Mathew

 

[DP]

The wire connected to terminal 2 must be the neutral or the boiler would not have worked when it was disconnected. So 2 goes to N.

DH have to disagree with your statement. OP already got the boiler working with neutral disconnected. The neutral is for use with the anticipator and has nothing to do with the boiler.

OP. The picture you downloaded which shows neutral wire lying disconnected. Well that wire goes to N not the switch terminal as shown later. Bit handicapped typing on the iPad or would have posted full details,

 

[benseb]

Tried with Grey as neutral first, no power to thermostat.

Is there anyway of testing if the Neutral is connected to anything without accessing the boiler? Surely if there is a voltage between Earth and the grey neutral this would indicate it's connected?

If so, what's up?

 

[MJN]

The voltage could be induced without being connected to anything.

Just sort the boiler access out, you're gonna need it one day! (Indeed, that day is arguably already here!)

Mathew

 

[DP]

Connect a bulb to the live and what you whink is the neutral. If the bulb/lamp lights, you are sorted.

The thing that eludes me is why are you messing about with a mains powered unit when a bettery equivalent would have sufficed (i.e. no need for a neutral)?

 

[Agile]

OK, I'll try - boiler has been boxed in and although I can get the top off, I can't pull the bottom part out which is where the cable runs into. Will have to get the tools out...

So how did the boiler get serviced ( or repaired ) ?

Tony

 

[ecowarrior]

Tony - what r u doing on this post? I cant believe what I reading. How many men does it take to change a light bulb? I have to go back to a better place and never return here.

 

[Agile]

Light entertainment!