Testing & Teaching
Digital Multimeter
In short
A digital multimeter measures volts, resistance and continuity, one at a time, on the setting you choose.
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
What it is
A DIGITAL MULTIMETER measures volts, resistance and continuity, one at a time, on the setting you choose.
Measure voltage with the circuit in use, with care. Measure resistance and continuity only on a circuit that is off and PROVED DEAD.
Heating engineers use an AUTO-RANGING meter: it picks the range itself. They need its direct current (DC) ranges too, for 24 V controls and for a THERMOCOUPLE in millivolts.
Check the function before every reading. GS38 warns of a meter left on a current or resistance range when you measure volts. On DC, it can read a live alternating current (AC) terminal as nothing.
This simulator's meter needs no DC setting. On volts (V~) it reads DC by itself where there is DC, such as an OpenTherm pair, and its screen says DC VOLTS. With the probes the other way round it shows a minus sign.
What the meter reads
Live to neutral, or live to earth: about 230 volts (230 V). Neutral to earth: about 0 V.
Continuity: a beep across an unbroken wire, with the supply off.
Ohms (resistance), dead: a wire reads a few ohms. A WINDING, an ELEMENT or a SENSOR reads its own figure: a valve motor reads about 2.40 kilohms in this simulator.
With nothing joining the probes, it reads OL: open, with no path.
Where it connects
Also in testing & teaching
Practise it in the simulator.
Runs in the browser on a laptop or desktop. Cancel any time.