Heating Wiring Problem - cylinder thermostat not working

[dfreitag]

Hi again, and THANKS SO MUCH for your time and for bearing with my being an amateur!

Cylinder stat: I've already answered this one. The neutral supply to the stat appears to be floating free and not connected to anything at the wiring box end. It's never going to work without power.

Gotcha! This was 100% working before the last wave of "professionals".. meaning one of them did this.. anyway..
(Just looking at this again, I've just noticed that both black cables from cable (2) on the right and from the CylStat bear the same (clumsy) black isolation tape - were they maybe connected before? )

Where should I connect it to at the wiring box to make sure it gets power again?

Also, is there anything you think I should change on the actual CylStat wiring, or should I leave this as is?

(I'm uploading a new marked up version of the previous photo for easy reference to each point of the wiring box.)

Nest wiring: The green/yellow appears to have been used for 'hot water on', since it's connected to 10 at the wiring box. Wires can be used for purposes other than that indicated by their colour if a short identifying sleeve is fitted over the wire at each end, BUT this does not apply to a green/yellow wire. This can only be used for earth and for no other purpose.
The cable used appears to be only 4 core, so should be replaced by 5 core, with the green/yellow used for the earth connection to the nest, and the grey (with brown sleeves at each end) used for 'hot water on'.

I'll get a 5-core and try to do as suggested.

Wiring box: The wires that are connected appear to be connected properly, but, as I've already written, the neutral for the 'stat isn't connected, and I suspect theirs also a green/yellow in that cable that has just been cut short.

Thanks for your feedback on proper connection at Wiring Box. At least that's ok!

Someone has definitely cut the earth on both sides of that cable. (This CylStat cable is actually a 4-core, but you can only see 3.)

I'll take it out again on both sides.

Can you please guide me as to where to connect the earth to properly (on both wiring box and CylStat)?


Many thanks!!

 

[dfreitag]

I've studied the pictures in detail but it looks like the cable from the wiring centre to the cylinder stat doesn't have enough cores in it. It should have a 5 core flex in order to connect it up in the traditional manner, how hard would it be to replace that cable?

That cylinder stat is unusual as it requires a permanent live and neutral supply whereas most don't so I suspect that is where this problem has arisen from.

No, don't go moving that green/yellow wire, it won't work at all if you do that. Whilst it is not right, it is not causing the problem.
Connecting the green/yellow of the two core flex to that earth terminal is unlikely to achieve anything either as the other end of that cable won't be connected to earth as it goes to the nest thermostat.

Thanks for your help davesparks.

brianmoooore already suggested I get a 5-core for the Nest, too, so I'll jusst get some more to replace the CylStat cable, too (and leave the earth as is for now..)

 

[brianmoooore]

Any wire or flex that contains an earth wire should have that wire connected at the wiring box end, whether or not that earth wire is connected to anything at the other end. The earth connection points at the wiring box are the lower three of the vertical connector strip, provided that the little wire links that connect the three together are in place. (E, F, G)
The disconnected black wire to the 'stat should be connected to any of the neutral terminals in the wiring box. These are the next three terminals up in the vertical connector strip, again assuming the wire links are in place. (B, C, D).

 

[dfreitag]

Any wire or flex that contains an earth wire should have that wire connected at the wiring box end, whether or not that earth wire is connected to anything at the other end. The earth connection points at the wiring box are the lower three of the vertical connector strip, provided that the little wire links that connect the three together are in place. (E, F, G)
The disconnected black wire to the 'stat should be connected to any of the neutral terminals in the wiring box. These are the next three terminals up in the vertical connector strip, again assuming the wire links are in place. (B, C, D).

Thank you - again!

Very clear. I'll give it a go now.

Earths to EFG

Black to BCD

Should I also connect the black one from cable (2) to BCD? (what is cable (2)?)

I'll report back after trying this..

 

[brianmoooore]

I wouldn't advice connecting the other black without knowing if or where the other end is connected.

 

[Aaron b]

Deleted... Didn't see the neutral links to the valves.

 

[brianmoooore]

One of your valves need to open to call the boiler and pump. Currently it doesn't have the blues connected, this is the neutral for the internal motors.

??????????? Both valve neutrals are connected to the lower neutral terminal, D.

 

[Aaron b]

??????????? Both valve neutrals are connected to the lower neutral terminal, D.

Sorry didn't see the look links at first. You caught me before I edited.

 

[dfreitag]

Hi.

Did as I was told (earth to EFG and black to BCD) and the CylStat is finally working again!!

Thanks again for all the input!!!

(Can I ignore the last message exchange with Aaron? )

 

[Aaron b]

Hi.

Did as I was told (earth to EFG and black to BCD) and the CylStat is finally working again!!

Thanks again for all the input!!!

(Can I ignore the last message exchange with Aaron? )

Yup, ignore my input. Glad you got it working.

 

[dfreitag]

Hi all

I was wondering - do you think it's worth re-wiring the CylStat, so it's on ALL the time, as suggested by it's manual? (and what would I need to do, to achieve this?)

At the moment it only switches on when switching on the hot water..


See below revised wiring box

Many thanks!
D

 

[Aaron b]

The green/yellow is the switched live from the stat, ideally that would fed the common of the thermostat which is currently done using the blue link wire within the stat. The brown conductor to the stat could the be moved to the permanent live terminal. You would need replace the flex for a 5 core as using the earth would be naughty...

 

[dfreitag]

To be honest, the cylinder stat was just the tip of the iceberg - just trying to solve things step by step..

My real problem is that my boiler seems to be overheating constantly, even though both heating and hot water are off.

After some discussions with the (somewhat questionable?) professionals mentioned previously, my understanding is that the following is happening:

The overheating causes the boiler pump to run almost constantly, as it tries to cool itself down.
(Observing it, I don't think it's actually firing up, but I could be wrong.)

While doing so it tries to pump water into the system. But with both HW and heating valves off, there's nowhere to pump to, so the pressure rises, and it get's stuck into a loop of doing the same over and over again.
This I can only assume is torturing the pump.


Seeing that the wiring has been rather sloppy, I'm suspecting that it might be a wiring mistake or the Nest that's causing the whole issue.

What do you guys think?

Photos of the current wiring box are just above and the Nest wiring, too.

Please let me know if you need further info, images or anything else for that matter..

MANY THANKS!
D

 

[davesparks]

While doing so it tries to pump water into the system. But with both HW and heating valves off, there's nowhere to pump to, so the pressure rises, and it get's stuck into a loop of doing the same over and over again.

There should be a bypass of some sort in the pipework to prevent this from happening, usually an automatic bypass valve these days.

Your system will always continue to run the pump for a while after the demand for heating and/or hot water has gone off and the valves have closed. This is known as a pump overrun and is there to prevent excess heat building up in the boiler immediately after the burner goes off.

 

[Aaron b]

The boiler (and perhaps the pump) should be powered from the orange core from the valves. Modern boilers control the pump for overrun functions.