I have a Cannon C60ETC cooker. Main oven running 30 degrees under when first delivered. Hotpoint replaced both thermistors and pc board. Main oven temp improved to within 10 degrees top oven spot on. 6 weeks later main oven reading 30 degrees under again. Another fault is main oven indicator does not indicate when temp is increased ( buzzer as in the case of top oven) Hotpoint coming again next week. Have I a rogue product??