Commissioning Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Most Commissioning Engineer interviews in the UK follow a pattern, and knowing it beats guessing. Below are eight questions from our bank of 16, each with a note on what the interviewer is really after.

Eight Commissioning Engineer interview questions, and what the interviewer is thinking

1. What does a commissioning engineer do, and how is commissioning different from testing and handover?

Why they ask: They want to see whether you understand the scope of the role and where it sits in a construction programme.

2. Which CIBSE and BSRIA commissioning guidance do you work to, and how do you structure the commissioning of a new system?

Why they ask: They want to know that you follow recognised procedures rather than improvising.

3. How do you balance a heating or chilled water system, and what is proportional balancing?

Why they ask: They want to see practical understanding of hydraulic balancing and how to approach it methodically.

4. How do you measure and balance airflow on a ventilation system?

Why they ask: They want to see knowledge of instruments, methods and the typical issues in air distribution.

5. What pre-commissioning checks do you require for a new pipework system before it is filled and put into service?

Why they ask: They want to see whether you understand cleaning, pressure testing and water treatment as the foundation of reliable commissioning.

6. How do you carry out point-to-point and functional testing of a building management system?

Why they ask: They want to know that you can verify controls properly, since many comfort and energy problems originate there.

7. Fully open dampers and a fan at maximum still leave airflow at 70 per cent of design. How would you investigate?

Why they ask: They want to see whether you can fault-find systematically instead of blaming the equipment or the designer straight away.

8. Tell me about a time you found the root cause of a commissioning problem that others had missed.

Why they ask: They want evidence of analytical thinking and persistence beyond routine measurement.

A sample answer to question 1

What does a commissioning engineer do, and how is commissioning different from testing and handover?

Commissioning is the process of advancing a system from static completion to full working order and proving that it performs as designed. That includes pre-commissioning checks, setting to work, regulating or balancing flows, adjusting controls, and demonstrating performance against the specification, then recording the results. Testing is part of it, but on its own only shows whether something passes at one point in time, while commissioning also involves setting and tuning. Handover comes afterwards: it is the formal transfer of the completed systems to the client, together with the O&M manuals, as-built drawings, commissioning records, warranties and training for the facilities team. On a day-to-day basis I plan commissioning sequences with the site team, check that systems are ready, carry out and witness measurements, log results and snags, and chase the trades to close out defects. I work closely with the designer to resolve any performance gaps, so the building meets the brief and is easy to operate afterwards.

Common mistake to avoid: Treating commissioning as just switching things on; confusing it with handover

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the Commissioning Engineer interview questions page. The first five are free, no sign-up needed.