Ahh, ok
This is a good, general guide
http://www.safelincs.co.uk/positioning-of-smoke-and-heat-alarms/
Heat alarms go off at 56°C. I wouldnt expect any of the wall or celing surfaces in your kitchen will get that hot.
Alarms come with installation instructions that tell you where not to put them. Have you not read yours??
Example:
DON’T place Smoke or Heat Alarms in any of the following areas:
• Places where the normal temperature can exceed 40°C or be below 4°C (e.g. attics, furnace rooms, directly above ovens or kettles etc.) as the heat/steam could cause nuisance/false alarms.
• Near a decorative object, door, light fitting, window moulding etc., that may prevent smoke or heat from entering the Alarm.
• Surfaces that are normally warmer or colder than the rest of the room (e.g. attic hatches). Temperature differences might stop smoke or heat from reaching the unit.
• Next to or directly above heaters or air conditioning vents, windows, wall vents etc. that can change the direction of airflow.
• In very high or awkward areas (e.g. over stairwells) where it may be difficult to reach the alarm (for testing, hushing or battery replacement).
• Locate away from very dusty or dirty areas as dust build-up in the chamber can impair performance. It can also block the insect screen mesh and prevent smoke from entering the smoke detector chamber.
• Locate the unit at least 1m from dimmer controlled lights and wiring as some dimmers can cause interference.
• Locate unit at least 1.5m and route wiring at least 1m away from fluorescent light fittings as electrical “noise” and/or flickering may affect the unit. Do not wire into the same circuit as fluorescent lights or dimmers.
