Heating Wiring Problem - cylinder thermostat not working Electrical Advice

Heating Wiring Problem - cylinder thermostat not working Discussion ThreadHeating Wiring Problem - cylinder thermostat not working Electrical Advice

Hi there,

I've had 4 plumbers & 1 electrician look at my problem (seemingly without dedicating too much time unfortunately), spending more than £1000 already 😣, but none of them has found the issue to my problem - that's why I'm reaching out to you!


I have the below set up

• 1x gas system boiler (Vaillant ecoTEC plus 624 R1) New Pump and New PCB installed rather recently
• 1x UNICYL HE indirect unvented 150L Cylinder
• 1x Cylinder Thermostat (ESI ESCTDEB ESCTDEB Electronic dual cylinder thermostat - https://www.esicontrols.co.uk/esctdeb.html)
• 1x Nest Thermostat (the "learning" type)
• traditional radiators

The Nest controls (or tries to) both heating & hot water.


At the moment the cylinder thermostat is not working - it just doesn't switch on anymore... (it used to only switch on when setting the Nest to boost hot water)

Thinking it was faulty I ordered an identical replacement, and replaced it myself.

By doing so I found the wiring to be rather odd - I have no prior experience at all with these things, so could obviously be wrong..


I am suspecting that someone messed up the wiring at one point.. Can you please have a look?


Many thanks!!


Central Wiring

Cylinder Stat Wiring

Cylinder Stat Wiring Instructions

Heating Wiring Problem - cylinder thermostat not working for the original thread on Electricians Forums