What is this?
Feeling a shock from a radiator or heating pipe means electrical current is flowing through your central heating system's metalwork. Like shocks from taps, this is caused by a fault elsewhere that is energising the pipework. The metal radiators and pipes act as conductors, carrying the fault current throughout the house. This is especially common in homes where the cross-bonding between electrical earth and pipework is inadequate or missing.
Common causes
- Missing or broken main earth bonding to the central heating pipework
- Faulty motorised valve, pump, or boiler leaking current onto the pipework
- Electric towel rail or radiator with an internal fault
- Damaged cable in contact with a heating pipe somewhere in the house
- Faulty immersion heater energising the hot water system and connected heating pipework
Is it dangerous?
This is dangerous and should be treated urgently. Metal radiators are large and easy to touch accidentally, especially for children. The fault current can be present on every radiator and pipe in the house. If the bonding is missing, the RCD cannot detect the fault, meaning there is no automatic protection against the shock.
Can I fix it myself?
Do not attempt to fix this. Turn off the mains electricity at the consumer unit. If you have an electric towel rail or electric radiator, check if the shock only occurs when that specific unit is on — if so, isolate it at its fused spur. Do not touch radiators or heating pipes with wet hands until the fault is resolved.
When to call an electrician
Call an electrician as soon as possible. This is a high-priority fault because it affects the entire heating system and could indicate missing bonding, which is a fundamental safety issue. The electrician may also recommend involving a heating engineer if the fault is in a boiler or motorised valve.
What will an electrician do?
Test all radiators and pipework for voltage
Check the main earth bonding and supplementary bonding connections
Test the boiler, pump, and motorised valves for earth leakage
Check any electric towel rails or radiators for internal faults
Restore or install bonding connections as required by BS 7671
Test the RCD to ensure it provides protection on the affected circuits
Typical cost
£100 – £280
Bonding repairs are relatively straightforward and at the lower end. If a boiler component or electric radiator needs replacing, costs will be higher and may involve a heating engineer as well.
