What does it mean if the RCD test button does not work?

Usually that the RCD has failed and may not cut the power in a real earth fault. It can also mean the button is broken or that side of the board has no supply. Either way, have an electrician test it with an RCD tester.

How often should I press the RCD test button?

BS 7671 asks for a notice at the consumer unit telling you to test six-monthly by pressing the T or Test button. The IET suggests doing it when the clocks change, so it happens twice a year. The RCD should switch off straight away; switch it back on afterwards.

Is it safe to use my electrics if the RCD will not test?

Lights and sockets will still work, but the circuits covered by that RCD may have no protection against electric shock. Avoid outdoor tools and appliances near water on those circuits until the RCD has been tested and replaced.

Can an RCD fail without me noticing?

Yes. An RCD can sit untested for years and seize, and nothing changes in day-to-day use. The test button is the only way a householder can find out, which is why regular testing matters.

What is the difference between an RCD not tripping on test and an RCD that keeps tripping?

An RCD that will not trip on test may have failed and is not protecting you. An RCD that keeps tripping is working and is detecting a fault on a circuit or appliance. They need different fixes, and the second is covered on the RCD keeps tripping page.

What is the difference between an RCD and an RCBO?

An RCD protects a group of circuits against earth leakage. An RCBO combines RCD and circuit breaker protection for one circuit, so a fault or a failed device affects only that circuit.

RCD Test Button Not Working

If pressing the T or Test button does not switch your RCD off, the RCD has probably failed and the circuits it covers may have no protection against electric shock. Do not keep pressing it. Avoid using outdoor or wet-area appliances on those circuits and book an electrician to test and replace it.

High risk

Blake FolgadoCo-founder, Tradehand

Published 1 February 2026Updated 22 September 2026

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What's happening?

An RCD (residual current device) watches for current leaking to earth, for example through a person touching something live, and cuts the supply fast enough to prevent most fatal shocks. Its test button creates a small deliberate leak inside the device. Press it with the power on and the RCD switch should drop to off straight away, turning off the circuits it protects. BS 7671 asks for a notice at the consumer unit telling occupants to test it six-monthly. If nothing happens, one of three things is true: the RCD mechanism has seized or failed, the button itself is broken, or that section of the board has no supply at all. The test button only proves the trip mechanism moves. It does not measure how fast the RCD trips, which is why an electrician uses an RCD tester to time it. An RCD that will not stay on when you reset it is a different fault, covered on the RCD keeps tripping page.

What usually causes it?

The RCD's internal trip mechanism has seized, often in a device that has never been tested
A broken or jammed test button
Internal electronic failure after a power surge or lightning strike
Damp or corrosion inside the consumer unit, often in garages and outbuildings
No supply to that side of the board, so there is nothing for the test to trip
Old age: RCDs are mechanical and wear like any switch

Is it dangerous?

Yes. An RCD that does not trip on test may not trip in a real earth fault either, which is the situation it exists for: someone touching a live part, a damaged cable, a wet appliance. Circuit breakers (MCBs) protect cables from overload and short circuits; they do not protect people from shock. Until the RCD is proven, treat the circuits it covers, especially sockets used outdoors and in kitchens and bathrooms, as unprotected.

Can I fix it myself?

1. Check the RCD is actually on: the switch should be up and the circuits it covers should have power. 2. Press the T or Test button firmly once. It should trip immediately. 3. If it does not, do not keep pressing or try to force it, and do not open the consumer unit. 4. Avoid using lawnmowers, pressure washers, outdoor extension leads and appliances near water on those circuits. A plug-in RCD adaptor adds protection for a single appliance in the meantime, but it does not protect the fixed wiring. 5. Note the RCD's rating and any labels so the electrician can bring a replacement.

When should you call an electrician?

Book an electrician promptly if the test button does not trip the RCD. Ask for the RCD to be tested with an RCD tester and replaced if it fails. Make it urgent if anyone has had a shock or tingle, if the board is warm or smells of burning, or if the consumer unit is old or plastic and has other faults. Electrical Safety First's advice is the same: if the test button does not work, get a registered electrician to investigate.

What will the electrician actually do?

Confirm the RCD has a supply and check the test button operates the mechanism
Test trip time and trip current with an RCD tester
Check the circuits it covers for earth leakage and insulation faults before re-energising
Replace the failed RCD with a compatible device, or advise on RCBO protection per circuit
Fit or renew the six-monthly RCD test notice at the consumer unit
Record the results so you have evidence the protection now works