Gas Boiler Tripping The Electrics

What's happening?

A gas boiler uses electricity only for its fan, pump, controls and ignition, but if any of that leaks current to earth, the RCD in the fuse board trips. It is not a gas fault. It is the same trip you would see with a faulty kettle, and it is a protection that is working. What is useful is working out whether the leakage is in the boiler or somewhere before it, because the person to call differs. If the trip stays off when the boiler is switched off at the spur, and returns when you switch the boiler back on, the leakage is in the boiler or its controls. If the trip goes off with the boiler isolated, the fault is the wiring or another device on the circuit. Electric boilers are a different page.

What usually causes it?

• Moisture inside the boiler from a leak or condensation reaching the circuit board or wiring
• A failing pump or fan motor leaking current to earth
• A damaged ignition lead, transformer or electrode wiring
• A faulty programmer, room thermostat, frost thermostat or cylinder wiring on the boiler's circuit
• A worn cable, loose spur connection or rodent damage between the fuse board and the boiler
• An old RCD or breaker that is oversensitive, or a boiler sharing a circuit with other equipment

Is it dangerous?

Yes, take it seriously. An RCD that trips repeatedly is protecting you from a fault that can pass current through the casing or pipework. Leave the boiler isolated until it has been checked, and do not hold the breaker on or replace it with a higher rating.

Can I fix it myself?

Switch the boiler off at the fused spur. Reset the trip once. Note whether it holds. Then switch the spur back on and see whether it trips immediately, when the boiler fires, or only when the heating comes on. Write that down. Do not remove the boiler casing. Do not test with the casing off.

When should you call a heating engineer?

Call an electrician if the trip goes off with the boiler switched off at the spur, or if other circuits are involved. Call a Gas Safe registered heating engineer if the trip only happens when the boiler is on and the circuit holds with the spur off. Tell them what you saw, since it halves the visit.

What will the heating engineer actually do?

• Isolate the boiler and test insulation resistance on the supply and the controls
• Check the spur, cable and connections between the fuse board and the boiler
• Test the pump, fan, ignition lead and transformer for leakage to earth
• Check the programmer, thermostat and frost thermostat wiring
• Dry or replace anything wet inside the boiler and find the source of the water
• Check the RCD and breaker rating and confirm the circuit holds with the boiler running

Who fixes this

• Boiler repair

Questions people ask

Sources & References

1. GOV.UK: Approved Document P, electrical safety
2. Vaillant: most common boiler problems