Help Please my Baxi combi 105E Fires up no problem but Temperature very slow to rise.When running only have 1.5 volts at the modulating coil on the gas valve.If I give this valve 9 volts from an external source then the flame goes high and the Temperature rapidly increases.but will not modulate automatically.Also when the boiler reaches set temperature it shuts down and the safety thermostat neon starts flashing