Heating Wiring Problem - cylinder thermostat not working

[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.