Heater tripping the RCD / earth leakage
A heater circuit trips its RCD/earth-leakage protection — often when cold and first switched on, or once it's been damp — pointing to leakage to earth from the element.
Safety first
Earth leakage from a heater is a real shock risk. Don't bypass the RCD. Isolate and prove dead before testing the element. Moisture + heater + earth leakage is dangerous.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Moisture in the element (especially when cold)
Most likelySheathed elements can absorb moisture; leakage is worst from cold and often clears as they dry out — but a steadily worsening one is failing.
- 2
Element insulation breakdown to sheath/earth
#2The element's internal insulation has broken down, leaking to its earthed sheath.
- 3
Damaged element / cracked sheath
#3A cracked or damaged sheath lets moisture and leakage paths to earth.
- 4
Wiring/termination leakage
Least likelyDamp or damaged wiring/terminations at the heater leak to earth.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeNote when it trips — immediately from cold, after running, or only when damp — and isolate the heater circuit.
A pattern (cold/damp) suggesting moisture vs a hard fault.
Cold/damp pattern → suspect moisture; test insulation and consider drying.
Trips hot/always → likely a hard insulation breakdown.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Heater tripping RCD
→ step 2 - 2decision
Is element insulation to earth/sheath healthy?
Yes→ step 3No→ step 4 - 3decision
Is the heater wiring/terminations dry and sound?
Yes→ step 5No→ step 6 - 4result
Element leaking — dry if moisture-related, otherwise replace.
- 5result
Re-test; if it still trips, re-examine the element under load.
- 6result
Damp/damaged wiring — repair/dry and reseal.
Common mistakes apprentices make
- Bypassing the RCD to keep the heater running — removing vital protection.
- Replacing an element that just needs drying (or drying one that's actually failed).
- Not isolating the element from wiring when testing.
- Ignoring a leakage reading that's steadily getting worse.
When to stop & escalate
A confirmed element insulation failure is a replacement. Never defeat earth-leakage protection. Recurrent moisture ingress points to a sealing/environment issue to fix.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
RCD / RCBO keeps tripping
An RCD or RCBO trips repeatedly — immediately on reset, randomly during the day, or only when certain equipment runs. The earth-leakage protection is doing its job; something is leaking.
Motor with low insulation resistance to earth
An insulation resistance test on the motor reads low to earth — a sign the winding insulation is degraded, damp, or contaminated, risking trips and failure.
Heater not heating at all
A heater (element, band, or bank) produces no heat — temperature won't rise, the process stays cold, despite the control calling for heat.
Learn the theory
How the gear and circuits behind this fault actually work.