Energy is flow times temperature difference.

Flow alone says nothing about heat delivered.

Flow and return temperatures give the difference.

A calculator combines them continuously.

That is why it is an assembly, not a device.

Most faults are in the parts around the flow sensor.

They are a matched, calibrated pair.

They are not interchangeable with stores sensors.

Replacing one alone destroys the accuracy.

Both must be replaced together as a pair.

They belong in specified pockets and orientation.

Substitution is a common and invisible error.

The meter reads plausibly and is entirely wrong.

Nothing about the reading looks unusual.

Sign conventions may hide it completely.

Check sensor positions at commissioning.

Label the pockets permanently.

It is found years later during a dispute.

Those that follow from charging somebody.

Approval and sealed installation are typical.

Periodic re-verification is set in law.

An expired meter may not be billable.

Requirements differ by jurisdiction.

Budget the recertification from the start.

On flow rate, never on pipe size.

Matching the pipe is the common error.

It puts normal running at the bottom of the range.

Accuracy is worst there.

Heat networks spend their lives at part load.

Size for the actual operating flow.

Straight lengths, and a strainer.

Upstream and downstream lengths are specified.

Debris damages flow sensors.

Isolation valves allow verification without draining.

Access for reading and sealing is required.

Design the installation, not just the meter.

Cumulative energy, plus flow and temperatures.

Remote reading avoids manual visits.

Retained interval data settles disputes.

Communication protocol should match the estate.

Confirm what the billing system can ingest.

Data nobody can read is not evidence.