Recirculation of fuel

A method of operating a gas turbine engine, the gas turbine engine comprising:

• a combustor;
• a primary fuel-oil heat exchanger arranged on a main flow path to receive fuel and transfer heat from oil to the fuel so as to raise a fuel temperature to between 120° C. and 180° C. on entry to the combustor;
• a secondary fuel-oil heat exchanger arranged on a bifurcation line to receive the fuel and transfer heat from the oil to the fuel;
• a fuel recirculation line arranged to recirculate at least some of the fuel on a fuel flow path from a first point on the fuel flow path to a second point on the fuel flow path, the second point being upstream of the first point;
• and
• a modulator valve arranged to modulate a flow of the fuel along the fuel recirculation line, wherein the method comprises modulating the flow of the fuel along the fuel recirculation line using the modulator valve, the first point is downstream of the primary fuel-oil heat exchanger, and the second point is upstream of the primary fuel-oil heat exchanger and upstream of an inlet to the secondary fuel-oil heat exchanger such that the inlet to the secondary fuel-oil heat exchanger is between the second point and the primary fuel-oil heat exchanger and, the first point is located downstream of an outlet of the bifurcation line rejoining, from the secondary fuel-oil heat exchanger, the main flow path, and the inlet branching from the main flow path to the secondary fuel-oil heat exchanger is upstream of both of the primary and secondary fuel-oil heat exchangers.