Boiler Fault Finder

Short Circuit

Short circuit: (dead test)

This test will ascertain the integrity of the internal resistance of the boiler and should read no resistance/infinity between L and N on the 3 amp fused plug top pins.

  • Set multimeter on ohms scale for resistance readings
  • First put black lead from multi meter to N pin on the boiler terminal strip and secondly put the red lead from the multi meter to the L pin on the boiler terminal strip

Should the resistance reading move, there is a dead short and a fault is present. Where the boiler supply is connected to a fused double pole switch, 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).

There are six internal boiler components to check and the L and N connections for each component must be removed individually and then the L and N at the 3 pin plug top or at the boiler terminal block must be measured again.

Components to check (in this sequence):

  • Pump
  • Fan
  • Gas valve
  • Diverter valve
  • Circuit board
  • Internal wiring loom (visual observation only)

Should the internal resistance measure infinity/no resistance when the component is disconnected, then the faulty component has been traced.
Should the resistance reading maintain moving when the component is disconnected, the dead short is elsewhere (further investigation needed in the above sequence).

short circuit mains test