A practical problem. A floor mounted boiler frp failed by cycling on and off rapidly with the main gas relay opening closing when there was no flame. This may be happening only when the igniter system is still hot. The main earthing is through the pilot gas tube, using an aluminum pipe with a brass olive into steel. There is considerable heat curve between the pipe and the steel electrode. Could a micro amp dc current be generating by the Seebeck effect to confuse the detection system?