Dear all;
I feel I need some ideas as to where the problem might be.
I have a Vaillant Combi ecotec plus 825, 1 zone 9 rads, 6.7kW heat loss CH system.
This is controlled by a WC SensoHome.
The issue is that the boiler registers incorrect delta on Flow & Return (ca. 8-9C drop) due to water constantly circulating on the internal bypass.
Radiators are balanced properly and each one returns a drop of 18-20degC.
When the return is coming to the boiler it is mixed with hot water from the Flow going on internal bypass.
Subsequently the NCT sensor for the return which is located after the bypass is reading much higher temp than the whole circuit drop actually is.
I have a differential thermometer and measuring the return right under the boiler is showing a drop of ca. 18deg. With higher flow temps it is closer to ideal 20deg. Yet when this is mixed with the flow on the internal bypass - this is then raised to only 8-9deg drop as per the temp sensor (at D.041 installers menu).
The bypass valve in the diverter has been fully screwed IN to force the flow to the RADIATORS rather than go on the internal bypass and this helped a lot (with the factory default settings it caused the flow going on the bypass so much that the drop was ca. 4-5 deg). So with this screwed all the way IN, it is much better and given the WC adjusts the flow to max 55C - the boiler is constantly in condensing mode, so we're kind of good here.
But still I believe the efficiency would be better if the actual Delta achieved in the circuit could be registered at the boiler return.
What can be done to remedy this issue of internal bypass letting the water circulate almost at its own whim....
I feel I need some ideas as to where the problem might be.
I have a Vaillant Combi ecotec plus 825, 1 zone 9 rads, 6.7kW heat loss CH system.
This is controlled by a WC SensoHome.
The issue is that the boiler registers incorrect delta on Flow & Return (ca. 8-9C drop) due to water constantly circulating on the internal bypass.
Radiators are balanced properly and each one returns a drop of 18-20degC.
When the return is coming to the boiler it is mixed with hot water from the Flow going on internal bypass.
Subsequently the NCT sensor for the return which is located after the bypass is reading much higher temp than the whole circuit drop actually is.
I have a differential thermometer and measuring the return right under the boiler is showing a drop of ca. 18deg. With higher flow temps it is closer to ideal 20deg. Yet when this is mixed with the flow on the internal bypass - this is then raised to only 8-9deg drop as per the temp sensor (at D.041 installers menu).
The bypass valve in the diverter has been fully screwed IN to force the flow to the RADIATORS rather than go on the internal bypass and this helped a lot (with the factory default settings it caused the flow going on the bypass so much that the drop was ca. 4-5 deg). So with this screwed all the way IN, it is much better and given the WC adjusts the flow to max 55C - the boiler is constantly in condensing mode, so we're kind of good here.
But still I believe the efficiency would be better if the actual Delta achieved in the circuit could be registered at the boiler return.
What can be done to remedy this issue of internal bypass letting the water circulate almost at its own whim....