We have recently moved into a house equipped with this boiler. When the boiler is working quite hard (eg CH is recently turned on and heating up), turning on a hot tap results in a very distinct bang and vibration through the pipework. Once the boiler has changed to DHW mode, it operates without making excessive noise / banging. Also, when the tap is turned off and the boiler reverts to CH mode, there is no banging noise.
Once the CH is operating at temperature and the boiler is working less hard (once it has been on for an hour or so), the noise does not occur on turning on a tap.
I have bled all the rads and made sure that the pressure in the system is correct. I have also used the "bleed" screw on the expansion tank in the boiler to purge air from that. However, the noise has not gone away.
I am sure that this due to something that happens exactly at the time one opens a tap. Sounds like the pump maybe experiences high back pressure when the diverter valve operates or something like that.
I do also wonder though about the expansion tank. In the install manual for the boiler, the valve on the expansion tank is called an "expansion vessel charging valve". Sounds more like one is supposed to push something (eg air?) *into* the tank via this valve rather than bleed air out. The valve also looks like a bicycle tyre valve rather than a rad bleed valve. Unfortunately, the install manual makes no further mention of how to use this valve.
Hence, anyone got any thoughts? Anyone know about how this expansion tank charging valve works? I also wonder whether I should see what happens if the pump speed is reduced (I think it is one "3" at the moment, but can be set to "2" according to the install manual - but the manual does not recommend this).
Any help much appreciated. I have used an on-line form to ask Vaillant about this, but got no answer.
Once the CH is operating at temperature and the boiler is working less hard (once it has been on for an hour or so), the noise does not occur on turning on a tap.
I have bled all the rads and made sure that the pressure in the system is correct. I have also used the "bleed" screw on the expansion tank in the boiler to purge air from that. However, the noise has not gone away.
I am sure that this due to something that happens exactly at the time one opens a tap. Sounds like the pump maybe experiences high back pressure when the diverter valve operates or something like that.
I do also wonder though about the expansion tank. In the install manual for the boiler, the valve on the expansion tank is called an "expansion vessel charging valve". Sounds more like one is supposed to push something (eg air?) *into* the tank via this valve rather than bleed air out. The valve also looks like a bicycle tyre valve rather than a rad bleed valve. Unfortunately, the install manual makes no further mention of how to use this valve.
Hence, anyone got any thoughts? Anyone know about how this expansion tank charging valve works? I also wonder whether I should see what happens if the pump speed is reduced (I think it is one "3" at the moment, but can be set to "2" according to the install manual - but the manual does not recommend this).
Any help much appreciated. I have used an on-line form to ask Vaillant about this, but got no answer.