Vaillant VR65: change from unvented cylinder stat to VR10?

[Onetap]

NO!!! THRICE NO!!!
The VR10 is INSTEAD of the cylinder stat, not in addition!

Err, no. See above. The VR10 and associated electronics control the cylinder temperature. The thermostat and high limit stat are still needed on an unvented cylinder, but are set 'out of the way' at a high temperature and so never need to operate under normal circumstances.

Boiler controls are done in a similar way. You can control a boiler with a BMS system or similar electronic controller, which monitors the temperatures with NTC thermistor sensors. However, you'd never disable the control and HL thermostats unless you were seriously stupid.

Stick to the good old S-plan and Y-plan, Corgiman. You'll go far.

It's a 3 month old resurrection of an ancient thread. I doubt anyone will be reading it now.

 

[gorty]

I realise this is an old thread, but figured anyone looking into this will be most likely to find this thread, also it continues on from the discussion above.

With the view to buying them, I've been reading the installation instructions for the products VR10 with UniSTOR, Ecotec plus 624, VRC430 and VR81. The instructions do not include wiring the tank 2-port valve via the overtemp cut-out. Doing so, it may seem, would provide an extra level of safety. I'm therefore assuming it's just not necessary as regardless if the NTC fails open-circuit or short-circuit, the DAC on the VR40 will sense either failure and signal for the VR61/65 to de-energise the 2-port valve at the tank.

My concern would be that fitters installing many different systems would become confused and attempt their own modifications to the system intended by Vaillant. Such modifications could have unintended consequences on the operation of the controls. I do accept it would fail-safe, but I'd be against modifying a system designed and verified by Vaillant engineers.

 

[Onetap]

The instructions do not include wiring the tank 2-port valve via the overtemp cut-out. Doing so, it may seem, would provide an extra level of safety.

I think you have made a mistake. The cylinder wouldn't get BBA certification unless the 2-port valve shut on power failure or overheat. The fault-finding flow chart in the installation instructions indicate the valve should be shut when the overheat device has operated.

Manuel, he say;

"The thermostat which controls the DHW temperature (1,fig. 10) is adjustable between 20 and 65 °C. The built in safety thermal cut out operates at 90 °C. Should the thermal cut out be brought into operation, the motorized 2 port valve will be operated and shut the primary flow to the cylinder. Press the reset button (2, fig. 10) to reset thermal cut out and motorised valve."