Wiring thermostat to Honeywell 2 port valve for failsafe

[harpss1ngh]

Hi,

So I have a Vaillant system as per my previous thread and I have now got a Vaillant VR 10 sensor in place of the thermostat strapped to the hot water pipe that goes to the taps (Is that the correct location or should it be the flow/return to/from the boiler?).

I have the existing cylinder thermostat still attached to the cylinder and want to wire it so if the temperature of the water gets too hot, the cylinder stat cuts power to the 2 port valve to shut it off.

How do I connect the thermostat (E + L + N) to the hot water 2 port valve which has 5 wires (E + L + N + Grey + Orange). The E +L +N are wired to the VR66 wiring center which opens the valve when the cylinder or VR 10 send a call for heat.


EDIT:

Should it be wired like this:

L wire from 2 port valve to L of Cylinder Stat. N wire from 2 port valve to N on the wiring centre, N of Cylinder stat to the L on the wiring centre? I.E wired in series?

 

[Leesparkykent]

Unless I'm missing something I take it is a unvented cylinder and by fail safe you mean using the vr10 or cylinder thermostat as a high limit thermostat and vice versa for control?

If this is the case then IMO you need a dry pocket on the cylinder with a Combined Control & High Limit Thermostat.

like this one Albion Water Heaters - SU013 - Combined Control & High Limit Thermostat

 

[harpss1ngh]

Hi,

Not quite. The Cylinder already has the original Thermostat control and High Limit Thermostat as required for G3 Building Regulations. I want to keep that to meet the regulations and so as to not invalidate my Cylinders 25 year warranty as well as for peace of mind, worst-case scenario, in case either the VR10 fail as well as the Boiler's own overheat cut off, 2 port valve stuck in open position, etc.

So I would like to wire the Thermostat (Control and High limit are wired together internally on mine) as Normally Closed, instead of usual Normally Open, to use it simply as a high limit stat only, and I could set the control to a higher temp such as 70 degrees and set the Vaillant controls target cylinder temp to something like 60 degrees. I assume the way it would be done is to wire as per my last edit in the OP, but just wanted confirmation. This has been suggested on an old post on a different forum, so I'm not the only person to think of doing it this way.


I want to use the VR10 as recommended by Vaillant with my Vaillant controls to modulate the boiler's Flow Temp. Now, if I had the Vaillant UniStor Cylinder, it comes with a dry pocket for the VR10. However the VR10, as quoted in Vaillants instructions "can be used as an immersion sensor or surface mount sensor. When used as a surface mount sensor, the sensor is secured to the forward flow pipe or the return pipe using the supplied tension band. In order to guarantee good heat transfer, the sensor is flat on one side.". I've read people having installed it on a pipe it in older forums and engineers with experience with Vaillant controls saying its fine to do so, but never exactly where. I know what the pipes on the Cylinder are for. So according to the above, would the best place be the Return Flow Pipe going back to the boiler?

 

[ermintrude]

Put it on the return. Flow will always be hot during loading. When the cylinder is satisfied the return gets hot and that's when u want it to cut out. As no further heat is being transferred into dhw