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THERMOSTATS & CONTROLS

Thermostat Temperature Is Wrong

A thermostat can read incorrectly because it is near a heat source, in a draught, badly calibrated, affected by sunlight or suffering a sensor fault.

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Isolate electrical power before opening controls, receivers or wiring centres

Heating controls may contain mains voltage. Basic settings and battery checks are safe, but internal wiring and relay testing should be handled by a competent person.

MOST LIKELY CAUSES

Start with these

Poor location Nearby radiators, kitchens or draughts distort the reading.
Calibration offset The control may be set to display above or below actual temperature.
Blocked airflow Furniture or covers can trap warm air around the sensor.
Sensor fault The internal temperature sensor may be inaccurate.
◫ Symptom variations Match the exact timing, display or response pattern. ⌄
  • Reading differs from room thermometer
  • Heating stops too early
  • Heating runs too long
  • Reading changes rapidly
  • Error stays constant by several degrees
✓ Quick checks Simple checks before removing covers. ⌄
  1. Check batteries and power.
  2. Confirm time, day and schedule.
  3. Cancel boost, hold, away and holiday modes.
  4. Create a clear heating demand.
  5. Check receiver or relay indicators.
1 Step 1 — Compare with a reliable thermometer Isolate electrical power before removing covers or touching wiring. ⌄

Place it nearby and allow time for both readings to stabilise.

2 Step 2 — Check location and airflow Isolate electrical power before removing covers or touching wiring. ⌄

Move obstructions and note nearby heat or draught sources.

3 Step 3 — Review calibration settings Isolate electrical power before removing covers or touching wiring. ⌄

Use any approved offset setting in the thermostat menu.

⌁ Common causes explained Why heating controls fail or behave unexpectedly. ⌄

A thermostat can read incorrectly because it is near a heat source, in a draught, badly calibrated, affected by sunlight or suffering a sensor fault.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Check sensor resistance or diagnostics.
  • Relocate thermostat.
  • Inspect wiring influence.
  • Update smart-thermostat firmware.
  • Replace failed sensor or control.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • Thermostat
  • Remote temperature sensor
  • Backplate
  • Wiring
  • Smart hub
! When to call a heating engineer Conditions that should end basic troubleshooting. ⌄
  • The control contains mains wiring.
  • The receiver or relay stays stuck on or off.
  • The heating ignores all controls.
  • A motorised valve or wiring centre may be faulty.
  • The boiler receives the wrong demand signal.
? Frequently asked questions Common thermostat and programmer questions. ⌄

Why does heating start before the set time?

Smart optimisation may start early so the room reaches temperature by the programmed time.

Why is the thermostat reading different from another thermometer?

Location, airflow and calibration can all affect the reading.