Viessmann Vitodens 100W permanently calling DHW cylinder

[GB1309]

[FONT=&quot]Hi everyone. I have traced out the wiring today and believe that my boiler is permanently outputting a "1" "call" to the Cylinder stat despite not being enabled by the on board programmer. This means the tank stat permanently sees a "live" and (if cold enough) holds the valve open permanently. The system is working fine apart from this anomaly. I have the DHW side of the programmer set for 3 x half hour slots per day and I would have expected the programmer to determine when the boiler (X1 L) goes live?[/FONT]
[FONT=&quot]My major concern is that the tank valve is being held open 24/7 and may take the motor out?[/FONT]
[FONT=&quot]Any help or advice gratefully received.[/FONT]
[FONT=&quot]Cheers,[/FONT]
[FONT=&quot]Graham[/FONT]

 

[joni os]

Check boiler stat is set higher than DHW cylinder stat. Are you on a four pipe system.

 

[GB1309]

Thanks Joni. Boiler stat is set to "dot" position which I believe is standard. Yes, I have a 4 pipe system.
Its running a Telford Tempest unvented so it has the cylinder demand box which converts mains signal from stat/valve to low voltage for boiler. I believe its all working correctly.
The ticketted guy that did the annual inspection on the cylinder pointed out the open valve yesterday but we checked that there was no consequent bleed over from the heating circuit and there isnt as the Y valve (presumably) in the boiler water block makes sure that only one circuit is fed at a time.
My boiler service guy is coming on Friday and I wanted to get as much diagnostics done as a I can in advance. Trouble is he did not wire the system as it was done by separate electrician. However if I can be sure that the programmer is the only means by which the boiler sends up to the stat then I can isolate the problem. I hope.
Sorry if this is a bit garbled, I'm a radar not heating engineer!
Cheers,
Graham.