I have recently noticed that the pump on my Vaillant boiler is running constantly even when there is no demand from either the DHW or CH. Everything seems to work ok when I require either DHW or CH but the pump will continue to run constantly after the event. The boiler has been fitted for approx 10 years and this has never been an issue before. Can anyone give me some pointers as to where to start looking for problems.

Tony., October 2006

Factory setting for the pump mode selector is 1. This will give pump operation on demand of the external controls. If you have no external controls (i.e. a link between 3 - 4 on the main terminal strip) the pump will run continuous. Position II is pump operation controlled by the boiler thermostat with a pump overrun of 20 seconds, position III is pump operation controlled by the heating switch on the facia. Finally position S is the same as II but with a pump overrun of 5 minutes. Position s is only on "hybrid" boilers. hope that helps!

andy, heating engineer. homer1981uk@hotmail.com, December 2006

Yes, ideally it should run on after the boiler shuts down. I cant remember exactly which position is the factory setting but I think it is 3. I will check that.

John, November 2006

Thanx for the advice, I found the pump settings on the main board eventually and hey presto the pump now only runs when the heating is switched on although I have no room stat just rad stats is that a problem in itself? Now the boiler just gets to temp and switches off, should the pump continue running under these circumstances as my previous one did?

Tony, November 2006

This boiler has three different pump settings and one of them is that the pump will run constantly if the room stat is calling for heat. Try turning the room stat down and see if the pump stops. It's not a fault to be honest as it's an installation setting.

john, November 2006