It’s 8am, the autoclave’s throwing a temperature fault or stalling out of cycle, and your morning list starts in an hour. This is the article we’d want a panicked practice manager to find. Five-minute checks first, what you absolutely shouldn’t try to fix yourself, the regulatory position on running it anyway, and how to think about repair versus replace if this keeps happening.
A B-type dental cycle runs at 134 to 138°C for at least three minutes (HTM 01-05’s own wording, set out in its procurement chapter at §10.23). Some machines also have a 121°C / 15-minute cycle for heat-sensitive loads. The fault shows up in one of three ways: the chamber never crosses the sterilisation threshold, the unit aborts mid-cycle with an error code, or the printout shows the holding phase dropped below band. Any of those is a cycle fail under HTM 01-05 §4.21, and you treat them all the same way.
Before you do anything else, take the machine out of clinical service. HTM 01-05 §4.21 is unambiguous:
“If the sterilizer fails to meet any of the test requirements, it should be withdrawn from service and advice should be sought from the manufacturer and/or maintenance contractor. Any instruments processed in an unsuccessful cycle should not be used.”
Any cycles since the last passing test go in the re-process pile. Note it in the logbook now while it’s fresh.
That’s the rule for two separate reasons. The patient-safety one is obvious. The regulatory one less so: CQC inspectors apply Regulation 15 of the Health and Social Care Act 2008 (Regulated Activities) Regulations 2014, equipment must be “suitable for the purpose for which they are being used” and “properly maintained”. A known-failing steriliser running clinical loads breaches both clauses regardless of whether anyone gets hurt. And under the Pressure Systems Safety Regulations 2000, operating a pressure system known to be defective is a criminal offence the HSE can prosecute on.
In order, before you ring an engineer:
Read the printout or display. Note the exact error code and the chamber temperature shown at the moment of failure. Have this written down before you call anyone, it shortens the engineer’s diagnosis by half.
Check the water reservoir. Empty or near-empty is the most common cause of a temperature fault on a benchtop autoclave. If you’re running the machine on distilled or RO water (and HTM 01-05 §4.20 says you should, “fill the reservoir with distilled water or RO water”), confirm the supply is actually getting through.
Check the door seal. Open the chamber, look at the seal. Is there a hair, a glove tip, a piece of pouch material caught in it? Is it visibly cracked, flat, or shiny? A door-seal leak lets steam escape during the heating phase, which means the chamber can’t reach saturation temperature. Wipe it with a damp lint-free cloth and reseat it if it’s slipped. HTM 01-05 §4.20 actually requires this as a daily pre-test check anyway.
Confirm the right cycle is selected. Sounds obvious. Happens regularly. A delicate-load cycle being run for a routine instrument tray, or vice versa, can produce confusing results.
Allow a full warm-up. If the machine’s been off overnight or for the weekend, the first cycle of the day on some models needs a warm-up run before clinical loads can be processed reliably. Check your manufacturer’s manual.
Check mains supply. A mains voltage drop in the building can stop the heating element pulling enough power. If something else just tripped in the practice, that’s worth investigating.
If you’ve worked through those five and the fault still presents, the next section is for you.
The rule is simple: anything that requires opening the case is engineer-only. Under the Pressure Systems Safety Regulations 2000, the autoclave is a pressure vessel with a Written Scheme of Examination, and work on the pressure system must be done by a Competent Person. Touching it yourself isn’t just unsafe; it’s a regulatory breach that affects your PVI certificate and likely your insurance.
Specifically, do not attempt:
If your diagnosis of the fault points at any of those, call an engineer.
In rough order of how often we see them in the field on benchtop dental units:
Limescale on the heating element. The single biggest hidden cost of running an autoclave on tap or hard mains water. Calcium and magnesium deposits build up on the element, insulate it from the water, and force it to run hotter to deliver the same energy. Eventually the element burns out or the chamber stops reaching temperature within the cycle window. HTM 01-05 §4.20’s requirement for distilled or RO water exists for exactly this reason. There’s a longer write-up on HTM 01-05 compliance in our HTM 01-05 validation guide.
Heating element failure. The natural end-of-life condition that limescale accelerates. Once the element’s gone, the machine simply can’t generate the heat. Replacement is a relatively standard engineer job for the supported brands.
Temperature sensor drift. The chamber’s actually reaching temperature, the sensor just isn’t reading it correctly. Validation picks this up if it’s been creeping; sudden failures present as fault codes.
Pressure transducer fault. The cycle’s logic depends on knowing the chamber pressure as well as temperature. If the pressure reading drifts, the cycle either won’t complete or won’t hit the right hold parameters.
Vacuum pump degradation (Type B machines). Failing vacuum means the pre-vacuum stage doesn’t pull down to the required level, which affects the subsequent heating phase too. Often shows as a combined “won’t reach temperature AND won’t pass the steam-penetration test” pattern.
Boiler or steam-generator scaling. On units with separate generators, scaled internals reduce steam quality and slow the chamber heat-up.
If this is the first time the machine has had a temperature fault and it’s under about eight years old, repair is usually the right call. Element, sensor, pump, seal: all replaceable components on the brands GQ services.
Replace becomes the right answer when:
A repaired autoclave needs full revalidation before it can go back into clinical service, HTM 01-05 §12.2 is explicit that “It will also be necessary to validate equipment after any major repairs have been carried out.” Don’t let an engineer fix the unit and walk away without that step.
For the CQC inspection trail, everything needs documenting:
That’s what an inspector wants to see when they ask “what happened the last time your autoclave failed?” The good answer demonstrates the practice noticed the fault, withdrew the unit, documented the action, and returned it to service properly. There’s a longer write-up of the inspection paperwork in our HTM 01-05 validation guide and the CQC inspection guide for practice managers.
If you’ve worked through the five-minute checks and the fault is still there, ring us on 01274 265566. Have the error code and the chamber temperature reading from the printout in front of you when you call, we can usually diagnose the likely fault category over the phone and tell you whether it’s a same-day call-out or a parts-return job.
For practices replacing a unit that’s at end-of-life, our three Class B ranges are on the practice equipment page, the Castellini C Series, Stern Weber SW Series and Mocom B Classic. Quoted with installation, commissioning, validation and the first year’s service in a single package.
