You are three quarters of the way through an EICR when you notice the calibration sticker on the tester expired in June. It is now August. Somewhere behind you are several jobs certified with that instrument.
This is a bad afternoon, and it is entirely avoidable, but the avoiding has to happen months earlier than the noticing.
The short answer
What happens if your tester is out of calibration?
The reading is not automatically wrong, but you can no longer evidence that the instrument was reading true on the day — so any certificate signed with it is much harder to defend if challenged. Consequences vary by scheme and trade. Ask your scheme provider rather than deciding alone.
Why calibration is not paperwork
A certificate is a statement that you measured something and it read a particular value. The instrument is the reason anyone should believe you.
Take away current calibration and the measurement is not necessarily wrong — it is unevidenced. You can no longer demonstrate the tester was reading true on the day. That is a different and much weaker position, and it is the position you are in if somebody challenges the result: an insurer after a fire, a solicitor after an incident, a scheme assessor on a routine visit, or simply the next contractor who finds something you signed off as satisfactory.
The practical consequence is not usually a fine. It is that the certificate stops being able to defend you.
What actually needs calibrating
Anything whose reading you rely on. Multifunction testers, insulation resistance testers, loop and RCD testers, clamp meters, gas analysers, pressure gauges, torque wrenches, moisture meters.
Not everything needs a full lab certificate every year, and requirements differ by trade, by scheme and by manufacturer. Two things worth separating in your head:
- Formal calibration — the instrument goes away, comes back with a certificate and a new due date.
- Ongoing verification — the checks you do yourself between calibrations, against a known reference, to catch drift early.
Your scheme provider or manufacturer sets the interval and the expectation. Do not take an interval from an article on the internet, including this one — take it from them, and then record it.
The failure is always the same
Nobody forgets calibration because they do not care. They forget because the due date lives in exactly one place: a fading sticker on the side of a tester that spends its life in a case in a van.
You see that sticker when you are already using the instrument. Which is to say, you see it at precisely the moment when noticing is least useful and most expensive.
The fix is not discipline. It is moving the date somewhere it can shout at you a month early.
Worth pinning down
What actually sets your interval
- Your scheme providerNot a universal rule. Confirm yours in writing and record it against the instrument.
- The manufacturerTheir stated interval is the floor, not the ceiling.
- Interim verificationMany trades expect checks between formal calibrations. They catch drift; they do not replace calibration.
- Enough notice to actAround a month is the practical minimum. ServicePay warns at 30 days.
Thirty days is the number that matters
A warning on the due date itself is nearly worthless. Calibration is not instant — the instrument has to go somewhere, sit in a queue, and come back, and you have to work without it while that happens.
A month of notice is roughly what it takes to do that without cancelling anything: book the slot, borrow or hire a spare if you need one, and schedule the jobs that need that instrument either side of the gap.
A month of notice turns a crisis into a diary entry. The due date itself turns it into a cancelled day.
If you have already certified with an out-of-calibration instrument
First, do not quietly carry on. The exposure grows with every additional certificate.
A reasonable order of events:
- Stop using it. Immediately, for anything you are going to certify.
- Establish the dates. When did calibration actually lapse, and which jobs fall after that date? This is the point at which having the instrument on a register with its history is the difference between an hour and a week.
- Get it calibrated. If it comes back in tolerance, that is meaningful supporting evidence that it was reading true across the period, even though it does not retrospectively make the certificates evidenced. If it comes back out of tolerance, you now know something important and unwelcome.
- Take advice before you act on affected jobs. Your scheme provider, your insurer or a solicitor, depending on the scale. What you should not do is decide on your own that it is fine.
- Write down what you did. A contemporaneous note of when you found it, what you stopped, and what you did next is worth a great deal later.
None of this is legal advice, and the right answer depends on your scheme, your trade and what was certified. The general principle holds regardless: find the boundary, stop adding to it, and take advice rather than guessing.
Record the date somewhere that is not the sticker
Whatever system you use — a wall planner, a phone reminder, a spreadsheet, or software — the requirements are the same:
- The due date is attached to the specific instrument, by serial number, not to a category of tool.
- Something tells you before the date, not on it.
- The calibration certificates are stored with the instrument’s record, so producing the history is one action rather than an archaeology project.
- It survives the loss of the van.
A phone reminder meets two of those four. It is still enormously better than the sticker.
How ServicePay handles it
Calibration lives on the same tool and equipment register as everything else you own, against the individual instrument and its serial number. Mark an item as requiring calibration, set the next due date, and it warns you 30 days out — and shows anything already overdue as overdue rather than burying it in a list.
Because the register also holds where the instrument is and who has it, the question “which jobs did we certify with that tester” starts from a record rather than from memory.
If you carry a scannable tag on the instrument, the calibration status can be shown on the public scan — so a client or site manager who wants to check can do it themselves with a phone, without ringing you.
Forty-two tools, and the two that need attention
The register is only useful when it tells you something. Two of these rows are doing work.
Tool & equipment register
42 items · replacement value £18,940
-
Calibration due in 9 days
Testo 557s flue gas analyser
Serial 557S-2210934 · Van 2 · bought 12 Mar 2024, £1,180
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Calibrated to 14 Nov 2027
Megger MFT1741 multifunction tester
Serial MFT-1741-08822 · Van 1 · bought 04 Aug 2023, £1,420
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No calibration needed
Hilti TE 6-A22 SDS drill
Serial TE6A22-887431 · Van 2 · receipt on file
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Hard to prove is yours
Makita DHR243 rotary hammer
No serial number recorded · no receipt on file
Why the red badge matters. An out-of-calibration instrument is grounds for challenging the certificate you issued with it. Nine days is enough time to send it away and get it back. Finding out afterwards is not.
Common questions
What happens if I issue a certificate using test equipment that is out of calibration?
The measurement is not automatically wrong, but you can no longer evidence that the instrument was reading true on the day, so the certificate is much harder to defend if it is challenged. Consequences vary by scheme and by trade — take advice from your scheme provider rather than deciding alone.
How often does electrical test equipment need calibrating?
Intervals are set by your scheme provider and the manufacturer rather than by a single universal rule, and many trades also expect interim verification checks between formal calibrations. Confirm yours in writing and record it against the instrument.
Does every tool need calibration?
No — only instruments whose readings you rely on when certifying or making a decision. A cordless drill does not need calibrating; the tester you used to prove the circuit was safe does.
Can I check calibration myself instead of sending it away?
Self-checks against a known reference are good practice for catching drift between calibrations, but they generally do not replace formal calibration where your scheme requires it. Treat them as an early-warning system, not a substitute.
How far in advance should I be warned?
Far enough to book the slot and work around the instrument being away. Around a month is a practical minimum; ServicePay warns at 30 days.