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FIXED APPLIANCES & DEDICATED CIRCUITS

Immersion Heater Not Working

An immersion heater may fail because of a blown fused-spur fuse, timer or switch fault, tripped thermal cut-out, failed thermostat, heating element or wiring problem.

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Stop if there is heat, burning, arcing, exposed parts or water near electrical equipment

Fixed appliances can draw high current and may remain connected even when their controls appear off. Do not remove covers or test exposed conductors. Leave affected circuits isolated and call a registered electrician or qualified appliance engineer where fixed wiring or internal faults are suspected.

MOST LIKELY CAUSES

Start with these

Blown fused-spur fuse A heater fault may open the local fuse.
Timer or control fault The immersion may not be receiving a switched supply.
Thermostat or cut-out tripped Overheating can stop the element energising.
Failed heating element The element may be open circuit or leaking to earth.
◫ Symptom variations Match the exact behaviour before testing. ⌄
  • No hot water from immersion
  • Fused spur indicator is off
  • Timer display works but water stays cold
  • Fuse blows when switched on
  • RCD trips during heating
✓ Quick checks Safe checks using controls and front-panel devices only. ⌄
  1. Check the appliance control panel, timer, thermostat and child-lock settings.
  2. Confirm the local isolator or fused spur is on and undamaged.
  3. Inspect the consumer unit for a tripped breaker, RCBO or RCD.
  4. Look for heat, smell, moisture, buzzing or discolouration.
  5. Attempt one controlled reset only if no danger signs are present.
If operation returns: monitor the appliance and circuit closely.
If the fault remains: leave the appliance or dedicated circuit off and arrange testing.
1 Fix 1 — Check the fused spur and timer Follow this check without opening live or fixed electrical equipment. ⌄

Process

Confirm the spur is on and the timer is calling for heat.

Success looks like: The immersion heats normally.
Failure means: If not, continue with circuit and appliance checks.
2 Fix 2 — Check the correct fuse once Follow this check without opening live or fixed electrical equipment. ⌄

Process

Replace only with the correct rated fuse after isolation.

Success looks like: The fuse holds and heating resumes.
Failure means: If it blows again, leave the immersion off.
3 Fix 3 — Check for another hot-water control Follow this check without opening live or fixed electrical equipment. ⌄

Process

Review cylinder thermostats, boost settings and programmers.

Success looks like: A control setting restores heating.
Failure means: If not, electrical testing is required.
⌁ Common causes explained Why the appliance or circuit may fail. ⌄

An immersion heater may fail because of a blown fused-spur fuse, timer or switch fault, tripped thermal cut-out, failed thermostat, heating element or wiring problem.

Fixed appliances often use dedicated circuits, high-current isolators, fused spurs or local controls. The fault may be in the appliance, the control accessory, the cable or the circuit protection.

⌘ Advanced diagnostics Technician-level testing for a competent electrician. ⌄
  • Test supply at fused spur and immersion terminals.
  • Check thermostat and thermal cut-out continuity.
  • Measure element resistance and insulation resistance.
  • Inspect cylinder-head wiring and terminals.
  • Verify timer, contactor and circuit protective device.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • BS 1362 fuse
  • Fused spur
  • Timer or programmer
  • Thermostat
  • Thermal cut-out
  • Immersion element
  • Cable termination
! When to call an electrician or appliance engineer Conditions that should end DIY troubleshooting. ⌄
  • The appliance or isolator is hot, burnt, buzzing or crackling.
  • The breaker, RCBO, RCD or fused spur operates repeatedly.
  • Water may have reached electrical components.
  • The appliance is permanently wired or high current.
  • The fault remains after simple control and supply checks.
  • Internal covers or fixed wiring would need to be opened.
? Frequently asked questions Common questions about fixed appliances. ⌄

Can the appliance be faulty even when the breaker stays on?

Yes. Controls, elements, motors and internal connections can fail without operating circuit protection.

Should I repeatedly reset a dedicated circuit?

No. One controlled reset is enough to confirm whether the fault remains.

Can I fit a larger fuse or breaker?

No. Protection must match the cable and appliance design. Increasing it can create a fire risk.