Ok so it's not really a long term solution then really I thinkYes, you could, but you would have to set the HW cylinder stat very high to keep the boiler firing, otherwise once the cylinder stat is satisfied then the boiler stops firing so no CH., If you are worried about a high HW temperature (children etc) then as a temporary measure you could set the boiler flow temperature to say 60C/65C. and the cylinder stat to 70C,