I am not a physicist however I am hoping some of you can help me out. We run biomass boilers in big supermarket stores so that they can appease the carbon levy and build ever more of them! One such boiler is behaving very strangely and defying all the laws of physics of my limited understanding. The boiler is running flat out in its boost mode trying to attain a set point of 78ºC. It has a furnace temperature of 700ºC which being a small 750kW boiler means this is the heat being transported directly through the heat exchanger. (water jacket surrounding a series of tubes through which the flue gas passes twice - 50% through the lower set and then reverses 50% through the upper set) The flue gas temperature (measured 500mm after the gas exits the heat exchanger) is 158ºC therefore the boiler is delivering 542ºC +/- to the heat exchanger. The delta T flow/return is only 1.8ºC and the boiler is only managing to produce a water temperature of max 62ºC. Prior to the last few days it has achieved its normal set point without having to run it flat out at a normal delta t 10ºC+/-. There is no back end three port valve on this system so its not blending the return and we have checked the primary and secondary pump speeds, they are as the original design parameters. The boiler is supplying 3 air handling units and approx 6 door curtains all of which have three port valves and heat exchangers. Any one got any idea as to whats going on? where is all this energy going to. All advice gratefully received.