Fluid warmer and method of operating a fluid warmer

A method for operating a fluid warmer for temperature control of a fluid flowing in a fluid tube, the fluid warmer comprising:

• a resistance heating element having a first and a second electrical supply connection conductor for connecting the resistance heating element to an alternating voltage source, the first electrical supply connection conductor having a first switch and the second electrical supply connection conductor having a second switch;
• a heat transfer element, which is thermally coupled to the resistance heating element for transferring heat to the fluid flowing in a vessel of the fluid tube;
• a functional grounding conductor connected to the heat transfer element for functional grounding of the heat transfer element, the functional grounding conductor having a third switch;
• a sensor for sensing a leakage current via the functional grounding conductor;
• and
• a control device for controlling the first, second and third switches;
• the method comprising the steps of:
• a) defining a maximum threshold current magnitude for a leakage current via the functional grounding conductor;
• b) comparing a leakage current measured with the sensor with the defined maximum threshold current magnitude;
• and
• c) putting the first, second and third switches into open switching states thereof within a defined time interval on occurrence of a leakage current, which is greater than or equal to the defined maximum threshold current magnitude.