viessmann boiler doesnt turn off

[coltmanneil]

Have a Viessmann vitodens boiler and generally we leave it on timed and it works fine.
However lately we have noticed on 3 occasions at night it has failed to turn off.I have changed the battery in the remote thermostate unit(vitotrol 100) and checked both the start/stop times which stay the same throughout the year.
Was wondering if at night if the remote unit was picking up a temperature that was "too cold" on the small dial hidden when white panel is shut.If this dial was saying the temp is too cold would the heating stay on.?????

When it had failed to stop I did the usual off/on on main boiler and all was well after that.
However it has happen a few times now.The boiler is 2 years old and still under warranty.
Help advice appreciated.
neilc

 

[stem]

If it's only happened recently during the very cold weather, you may have a frost thermostat somewhere. A frost thermostat overrides the timer and turns the boiler on when the temperature drops low enough to cause a risk of freezing. These are sometimes located in the roofspace or an outhouse if that is where the boiler is located. Generally there is a pipe thermostat that turns the boiler off again when the return pipe has got warm, but I have seen several installations where this part is omitted.

This wouldn't explain turning the boiler on/off curing the problem though, unless the stat just happened to be satisfied when you did it, or the pipe stat is on a high setting and mounted too close to the boiler, so that stopping the circulation allowed residual heat to be conducted back to the pipe stat and 'satisfying' it.

The only way to be sure is to follow the live signal from the controls that signals the boiler to run, from the boiler backwards to find out where it is coming from. If the boiler isn't getting a 'run' signal from the controls then the boiler is at fault.

Sometimes wireless controls don't always have connections that are 100% effective too, particularly if the transmitter and receiver have obstacles or long distances to overcome. Check out their instructions for details. Some allow you to change frequencies in case something else is interfering with them.

 

[coltmanneil]

Thanks Stem,

We are carrying out a few tests at present with this remote control unit.

Let you later what we find.

NeilC