Band / cartridge heater burnt out or underperforming
A band or cartridge heater (e.g. on a barrel or die) isn't reaching temperature or has failed — one zone stays cold or lags while others are fine.
Safety first
Band/cartridge heaters operate at high temperatures. Prove dead and allow cooling before handling. Confirm the correct zone is isolated.
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.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
Open / burnt-out heater
Most likelyThe band/cartridge element has failed open and draws no current.
- 2
Poor contact / loose fit to the surface
#2A band heater not clamped tightly, or a cartridge in a worn bore, transfers heat poorly and lags.
- 3
Degraded element (partial)
#3The element has risen in resistance and draws less current, so the zone underperforms.
- 4
Connection / lead failure
#4The heater's leads or terminations have failed where they flex or get hot.
- 5
Zone switching/control fault
Least likelyThe SSR/contactor or controller for that zone isn't driving the heater.
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.
Compare the affected zone's current/behaviour to a known-good zone while heat is called.
Similar current/heat-up to a healthy zone.
Draws like a good zone but lags — suspect poor contact/fit.
Low/no current — check switching, then the element/leads.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Band/cartridge zone cold
→ step 2 - 2decision
Does the zone draw current like a good zone?
Yes→ step 3No→ step 4 - 3result
Draws fine but lags — check fit/clamping and leads.
- 4decision
Is the zone's switching device driving it?
Yes→ step 5No→ step 6 - 5result
Element open/high — replace the heater.
- 6result
Switching/control fault for that zone — address it.
Common mistakes apprentices make
- Not comparing against a known-good zone.
- Missing a loosely-clamped band heater that heats poorly.
- Overlooking lead/termination failure where they flex or get hot.
- Assuming the element when the zone's SSR/control is at fault.
When to stop & escalate
Repeated failures in one zone suggest a fit, rating, or control problem to address rather than just swapping heaters. Process-temperature impacts may involve production.
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.
Related faults
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.
Heater bank drawing uneven current across phases
A multi-element heater bank pulls noticeably different current on each phase. Heating is uneven, output is low, or a phase reads much lower than the others.
SSR not switching on (load won't energise)
A solid-state relay won't turn its load on even when commanded — the heater/load stays off because the SSR isn't conducting.