Resistance to earth: (dead test)
This test confirms the integrity (resistance) of the insulation between L (Live) and E (Earth) on the boiler terminal strip or plug top pins (Black lead firstly to Earth pin and red lead secondly to Live pin).
Check CAREFULLY that the boiler is dead. At the boiler electrical connection, check that the L-N, L-E and N-E all read zero volts. Any reading at all and the boiler is not safely isolated.
Where the boiler supply is connected to a fused double pole switch (DPS), it should be isolated at the ring main supply end, to eliminate any possible, further faults present on the circuit (This is why a 3 pin plug is a much better option as a double pole spur can cause further problems).
- With the boiler switches, time switches and thermostats ON and the multi-meter set on Ohms scale, the resistance reading between Live and Earth should read “0L” ( infinity ) and if so, there is a fault.
- If there is a positive reading there is no fault.
A detailed continuity check is required to trace the faulty component before proceeding any further.
Other boiler fault checks to make
As a member check out these Key Areas
- Sequence of boiler operation
- Boiler servicing procedures
- Boiler System Component Testing
- Top Tips for the Heating Engineer
- Boiler Manuals and Service Manuals
- General Boiler Fault Finding
- Boiler Error Codes
- Using Multimeters to diagnose Boiler Faults