Hi @Barrie
Based on the real word testing we’ve done, a 7kW Vaillant should be about to output about 7kW even under the worst conditions. So it should be able to cover your 6.8kW calculated heat loss, your actual heat loss is probably lower.
If your heat pump is struggling to maintain the indoor temperature then you probably need to increase your WC setting, 0.3 is very low. As a test when it’s around 0C outside try setting to WC to max i.e 4.0 and the room set point to 30C, this will make the HP work as hard as it can, if this still fails to heat your house then the heat pump is undersized.
If after increasing the WC curve, the HP is able to provide sufficient heat, then the defrosts are nothing to worry about. Overall, the amount of heat lost via a defrost cycle is relatively low.
Would you mind removing the screenshot from your post? It’s quite very confusing for other forum users to see a screenshot of data which has nothing to do with your system! With a WC of 0.3 your flow temperature will only be reaching a maximum of 30C at 0C outside, the screenshot above shows a flow tempo of 45C at 10C outside.
