Home › Heating › Heating Won’t Turn Off

THERMOSTATS & CONTROLS

Heating Won’t Turn Off

Heating that stays on can be caused by a stuck thermostat, failed relay, jammed motorised valve, wiring fault or an active frost-protection function.

⌁
!

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

Thermostat stuck calling The control may not cancel demand.
Motorised valve stuck open The boiler may keep receiving a heat request.
Relay welded closed A receiver or programmer relay may remain energised.
Frost protection active The system may run automatically in cold conditions.
◫ Symptom variations Match the exact timing, display or response pattern. ⌄
  • Radiators stay hot
  • Boiler continues after timer ends
  • Receiver light remains on
  • Heating stops only at boiler
  • One zone remains permanently open
✓ 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 — Lower the thermostat fully Isolate electrical power before removing covers or touching wiring. ⌄

Set it well below room temperature and wait for response.

2 Step 2 — Cancel manual overrides Isolate electrical power before removing covers or touching wiring. ⌄

Turn off boost, advance and temporary hold functions.

3 Step 3 — Check receiver or valve indication Isolate electrical power before removing covers or touching wiring. ⌄

See whether the demand light or valve position remains active.

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

Heating that stays on can be caused by a stuck thermostat, failed relay, jammed motorised valve, wiring fault or an active frost-protection function.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Test thermostat output.
  • Inspect relay contacts.
  • Check motorised valve microswitch.
  • Inspect wiring centre.
  • Verify boiler frost logic.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • Thermostat
  • Receiver relay
  • Motorised valve
  • Programmer
  • Wiring centre
! 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.