Viessmann Vitodens. Hot weather, no hot water

[frogisland]

Turned the cylinder stat up but it didn't fire the boiler. Been ok since installation (6 years ago). Problem started towards the end of that hot period last year - maybe had a week of it, then forgot about it (when the day temp cooled back down) until just now with the last couple of hot days. I need to get the boiler serviced also.

 

[townfanjon]

Turned the cylinder stat up but it didn't fire the boiler. Been ok since installation (6 years ago). Problem started towards the end of that hot period last year - maybe had a week of it, then forgot about it (when the day temp cooled back down) until just now with the last couple of hot days. I need to get the boiler serviced also.

If the heating is ok there can be much wrong with the boiler

 

[frogisland]

If the heating is ok there can be much wrong with the boiler

Can't be?

 

[townfanjon]

Can't be?

Yep sorry cant lol

 

[EPH]

sounds like weather comp is holding the boiler off

@townfanjon

Why would weather come hold hot water off

 

[ShaunCorbs]

Why would weather come hold hot water off

If it’s not hot water priority and just simple controls it won’t know if heating or hot water is being demanded so will just run in wc mode

 

[townfanjon]

Why would weather come hold hot water off

It shouldn’t

 

[townfanjon]

I wonder if this has the v cylinder demand box installed , thats why I asked how long it had been installed for .

 

[frogisland]

Update

Boiler fired up for hot water during the night when it was cooler. Just now (09.30) not firing up for hot water. Outdoor temperature sensor is on a north facing wall, current temperature just below 26 degrees. Disconnected the cables from the sensor, resistance measured about 4.25KOhms, should circa 9KOhms according to the manual data @ 25 degrees.

Left sensor disconnected, switched boiler back on and it fired up for hot water.

However, just talked to Veissmann, they said very likely not the sensor itself. For the outside temperature sensor to work properly there should be a cylinder demand control box wired in (there isn't). Suggested leave the sensor disconnected. When i get an engineer in i'll have the wiring looked at. It was installed as part of a large extension about 5 years, i remember the contractors electrician struggling integrating with the existing electrics + outside sensor! (he didn't understand what the pump over-run did also + also other issues with the lighting circuit).

View attachment 39680

 

[townfanjon]

should be a cylinder demand control box wired in (there isn't).

I did wonder .
However , theres still something else wrong , because its worked up until now